Built by people who will not be there to use it
The compound is laid out by an enabling works gang in the fortnight before anybody else arrives, and almost nobody who builds it stays to live in it. That is the whole problem in one sentence. The platform gets whatever stone was already on site, the cabins get craned into the position the crane could reach, the supply gets terminated where the meter cabinet happened to be, and the laydown gets the leftover rectangle — and then two hundred people work inside those four decisions for the next two years.
Two of them are worth doing arithmetic on before the wagon arrives, because both are expensive to reverse and neither is obvious by eye. The first is the connected load on the temporary supply: get it short and the cabin trips out on the first cold Monday when the heaters, the kettle and the dryer are on together, and the fix is an outage and a new head. The second is what the laydown actually holds, which is never the number you get by dividing its area by a pallet, and the fix for that one is a second compound somewhere less convenient.
Everything else in a compound — where the gate sits, which way the cabins face, whether the smoking shelter is upwind of the drying room — is a judgement you can revise in an afternoon. These two are not.
One rectangle, four jobs, four different demands on the ground
A compound reads as a single fenced area on the logistics plan and behaves as four separate ones underfoot. What each part is being asked to carry is different in kind, not just in magnitude, and the mistake that follows from ignoring that is always the same: one specification of platform is built across the whole rectangle, and it is simultaneously too much under the parking and not enough under the cabins.
The distinction that matters is between a bearing surface and a running surface. Bearing is about settlement under a load that sits still for months; running is about rutting under wheels that pass over the same line four hundred times. A cabin corner jack punching slowly into a platform that carries forklifts perfectly well is the classic version, and it announces itself six weeks in as a door that has stopped latching.
| Zone | What stands on it | What the ground has to give |
|---|---|---|
| Cabin stack | Office, welfare and drying units on jacks or blocking | Point loads at four to eight jacking positions, and a bearing that does not settle differentially |
| Laydown | Stacked pallets, stillages, drums, reels, cut steel | Near-uniform bearing over a wide area, plus a surface a forklift can turn and brake on |
| Parking and delivery turning | Vans, small rigids, the occasional artic tail swing | Repeated wheel passes on the same line — a running surface, not a bearing one |
| Fuel and small plant store | Bowsers, bunded cabinets, breakers, compressors | Fall to a controlled point and a surface a spill does not soak into |
The platform under all of it
A compound platform is a granular raft: stone thick enough that the pressures reaching the subgrade stay below what the subgrade can take, laid over a fabric that stops the two mixing. It is not a pavement and it does not need to be one. It needs to survive the wettest month of the programme with a forklift on it, and it needs to come up again at demobilisation without taking three hundred millimetres of clay with it.
Thickness is not something to take off a rule of thumb, because the input that drives it is the strength of the subgrade you happen to have. Unsurfaced haul road and working platform thickness design belongs to published methods — the Giroud–Han method for geogrid-reinforced unpaved roads is the one most often referenced, and in Britain the BRE report BR 470, Working platforms for tracked plant, is the document a piling contractor will ask for by name before they bring a rig onto your compound. Both need a measured subgrade strength as their starting point, which is a CBR or a shear strength from a site test, not a description of the soil. What the arithmetic on this page does is turn the thickness someone has designed into a delivered tonnage.
The fabric underneath earns its keep in a way that is invisible until it is missing. Its job is separation: keeping the fines of a soft subgrade out of the voids of the stone, because once they migrate up the stone stops being free-draining and the platform behaves like the soil it was built to bridge. AASHTO M 288, Geosynthetic Specification for Highway Applications, is the specification that classes separation geotextiles and sets the overlap they need against subgrade strength — and it is the overlaps, not the plan area, that decide how many rolls come to site. Compaction gets tested against a Proctor density from ASTM D698 or ASTM D1557 in exactly the way a permanent pavement would; the platform being temporary changes the programme, not the physics.
How a compound platform is built up
- Stacked load on dunnage — the reason the platform exists, and the only layer whose weight arrives after everybody has stopped checking the ground Timber Pallet Stack Storage Capacity Calculator
- Compacted stone platform — bought by the tonne against compacted thickness, and battered back at the shoulder because a vertical stone edge ravels under the first wheel that clips it Gravel Base Layer Tonnage Calculator
- Separation geotextile — lapped by the amount the subgrade strength calls for and turned up past the stone edge, so the shoulder is where it works hardest Driveway Separation Geotextile Roll Calculator
- Prepared subgrade — proof-rolled and tested before anything covers it, because every thickness anybody designs was derived from its measured strength Standard/Modified Proctor Compaction Percentage Calculator
With a designed compacted thickness and the platform area measured off the ground rather than the plan, this converts the layer into the tonnage a haulier can quote against.
The total area to be covered with gravel base.
The target compacted thickness of the base layer.
The in-place density of the base once it is compacted.
Gravel base needed
73.8 tons
Actual density varies by material gradation and compaction — confirm with your supplier's specific product density for a precise order quantity.
- Volume
- 39.81 yd³
- Equivalent in US (short) tons
- 73.82 tons
They open the calculator with your figures already in it
Gravel Base Layer Tonnage Calculator: 73.82 tons — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- This is a take-off, not a pavement design. It multiplies out whatever compacted thickness you enter; nothing here derives that depth from traffic loading, subgrade strength, drainage or frost depth, which come from a pavement design or your local road authority's standard.
- Geometry is a flat plan area at one uniform depth. Crown and cross-fall, a formation that steps between thicknesses, a dig that deepens where the subgrade was soft, and edge thickening or haunching at the perimeter all fall outside area x thickness.
- No waste, spillage or subgrade-loss allowance is applied. The figure is the exact in-place mass, so stone lost into a soft or uneven formation, over-excavation, haul and spread losses, and the tail end of a part-load all sit on top of it.
- The density field is an in-place compacted density. A supplier's loose bulk density and a weighbridge ticket carrying free moisture are different quantities, and substituting either moves the tonnage: the wetter the delivered material, the less dry stone a given delivered weight puts on the ground.
- It covers one layer of one material. A base and sub-base of different gradations, a bedding or blinding course, and the geotextile or separation membrane between stone and subgrade are not counted here.
What the cabin actually draws
Temporary supplies get ordered against a figure somebody remembers from the last job, and the last job had a different cabin, a different winter and a different number of people charging things. The honest way to size it is to walk the cabin schedule and read nameplates, because everything in a site office has one: the split unit on the gable, the panel heaters, the water heater in the welfare unit, the LED battens, the printer, the drying room's fan heaters.
Group them the way the arithmetic wants them. Lighting is the easy one and usually the smallest. Heating and cooling is the one that swings hardest between June and January, and it is worth entering the winter case rather than an average, because a temporary supply is sized once. Receptacle and equipment load is the category people underestimate by the widest margin — not because the office kit is heavy, but because of what quietly plugs into a cabin ring: a 2 kW fan heater under a desk is on its own larger than most people's whole receptacle allowance, and there is one under a desk in every site office in the world by the second week of November.
What the calculation gives you is a straight connected-load sum with no diversity applied, and that is deliberate. Permanent installations apply demand factors because a house does not run its cooker, its shower and its immersion heater at once. A site cabin on a cold Monday morning genuinely does run everything at once, so the conservative sum is the right sum here. NFPA 70, the National Electrical Code, deals with temporary construction power in Article 590, Temporary Installations, and that article — not this arithmetic — is what governs conductor sizing, ground-fault protection for personnel and the disconnecting means. In Britain the equivalent is Section 704 of BS 7671, Construction and demolition site installations, sitting alongside HSE guidance HSG141, Electrical safety on construction sites.
Two corrections to apply after the division. First, a connected-load amperage is not a breaker size: the Code's continuous-load rule requires the overcurrent device to be rated at not less than 125% of the continuous load, so the calculator's own default case — 1,500 plus 3,500 plus 2,000 VA, giving 7,000 VA and 29.2 A at 240 V — is not a 30 A supply. Multiply by 1.25 and it is a 40 A one. Second, dividing by 240 V gives the figure for a balanced service. A cabin whose heaters, kettle and water heater all landed on the same leg of a 120/240 V split-phase panel draws far more on that leg than the sum suggests, and that is a panel-balancing problem the total cannot see.
Three nameplate totals and the service voltage give the raw connected amperage the cabin presents — the number to take to the electrician and to the supply application, before the continuous-load multiplier is applied to it.
The total connected lighting load in the site trailer, in volt-amps.
The total connected heating/cooling equipment load, in volt-amps.
The total connected load from receptacles, computers, printers, and other plugged-in equipment, in volt-amps.
The service voltage supplying the trailer.
Required service amperage
29.2 A
This is a simple connected-load sum with no demand factor applied — NEC Article 590 (Temporary Installations) governs the actual code requirements for temporary construction power, including conductor sizing, GFCI protection, and disconnect requirements, which this calculator does not address. Round up to the next standard breaker/service size and consult a licensed electrician for the actual installation.
- Total connected load
- 7,000 VA
They open the calculator with your figures already in it
Temporary Site Trailer Electrical Load Calculator: 29.17 A — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 29.2 A — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Divides the whole load by the voltage, which only gives the per-leg current if the load splits evenly across both legs of a 120/240 V supply. It never does — the lighting, receptacles and office gear are all 120 V and land wherever the panel schedule puts them. A trailer that computes 29 A total can be pulling 40 A on one leg and 18 A on the other, and the leg is what trips.
- Connected load is not breaker size. A continuous load is sized at 125 % for the overcurrent device, and the trailer's air conditioner pulls several times its nameplate for the first second of every start. This figure is what the equipment eats while running, not what the breaker has to survive when the compressor kicks in on a hot afternoon.
- If a generator is feeding the trailer rather than a temporary pole, amperage is the wrong question. A set is rated in kW at a stated power factor, and it is the motor starting kVA of the air conditioner that sizes it — a genset matched to the running load sags and stalls on AC startup, and the office reboots with it.
The months before the real supply turns up
Applications for a metered temporary supply are quoted in weeks and delivered in months, and the compound is occupied long before that. So the first phase of almost every job runs on a generator, and the generator is chosen by whoever answers the phone at the hire desk. Size it off the same connected-load exercise rather than off the cabin count, then add the starting current of anything with a motor in it — a split air conditioner drawing a modest running current still asks for several times that for a fraction of a second, and a set that is comfortable on running load can stall on it.
Fuel is the part that turns into a site management problem rather than an engineering one. A set that runs a compound overnight is refuelled on a rhythm somebody has to own, and the interval falls out of the tank capacity against the consumption at the load fraction it actually sees — which for a compound at three in the morning is very light, and a diesel set running lightly loaded for long periods wet-stacks and fouls. The usual answers are a smaller set for out-of-hours, or a hybrid battery unit that carries the night and lets the engine off. Whichever you choose, the bowser and the bunded store belong in the fuel corner of the compound with the containment fall built into that part of the platform, not added to it afterwards.
The distance between the supply and the cabin door
Compounds are long and thin, because they get whatever strip is left along a boundary. The head is at one end and the office is at the other, and the cable between them is the part of the temporary installation nobody sizes because it is not a fixed installation and it was never on a drawing. Then the office runs at a voltage that makes the printer restart itself and the split unit run hot, and everybody blames the printer.
The physics is unforgiving on length. Take a 30 A cabin feed at 240 V run 60 m from the head to the cabin door. On 10 AWG copper that is about 14.7 V dropped in the run, over six per cent, and the cabin sees roughly 225 V. Move the same run to 6 AWG and the drop falls to about 5.8 V, under two and a half per cent, and the cabin sees 234 V. Nothing changed except the copper, and the second one is the difference between equipment that lasts the job and equipment that goes back on the hire docket.
Voltage-drop limits are guidance rather than prohibition in both major codes, which is exactly why they get ignored. BS 7671 gives its figures in Appendix 12 — three per cent for lighting and five per cent for other uses, for an installation supplied directly from a public distribution network — and NFPA 70 carries the same three and five per cent figures as informational notes rather than as requirements. Treat them as a design target anyway. On a temporary installation the run is usually longer than a permanent one, frequently in flexible trailing cable rather than in a fixed wiring system, and the cable is coiled on a drum for half its length, which is a separate derating question about heat rather than about volts.
Feed it the walked distance from the head to the cabin, not the straight line on the plan — the cable goes round the laydown, and the run is the number that sets the drop.
Copper, or aluminum — the metal printed on the jacket (CU or AL).
The size printed on the jacket: an AWG number up to 4/0, then kcmil.
Single phase — including a 240 V circuit and DC — or a balanced three-phase circuit.
The distance from the panel to the load, one direction only.
The expected current draw of the load in amps.
The nominal circuit voltage — line to line for three phase.
Voltage drop
1.936 V
- Voltage drop
- 1.61 %
- Voltage at the load
- 118.06 V
- K constant, Ω·cmil per ft
- 12.9
- Conductor area, circular mils
- 6,530
They open the calculator with your figures already in it
Wire Gauge Voltage Drop Calculator (Copper or Aluminum, AWG to 1,000 kcmil): 1.94 V — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 1.936 V — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- VOLTAGE DROP IS NOT AMPACITY, and the two are different questions with different answers. A conductor can stay inside the 3% suggestion and still be too small to carry the current without overheating, and it can be thermally adequate and still drop too much over a long run. Both checks have to be made, and only one of them is made here.
- The K constants are DC resistance at 75 °C (167 °F) for uncoated copper and for aluminum, the basis of NEC Chapter 9 Table 8. The table's size-by-size resistances differ from the single constant by a percent or so either way, and the table is not reproduced here. A conductor running cooler drops a little less and one at a 90 °C (194 °F) rating a little more; tinned (coated) copper has its own, slightly higher resistance.
- Treats the circuit as resistive, which is close for lighting, heating and most branch circuits. On a large AC feeder, and above all one in steel conduit feeding an inductive load, the conductor's reactance adds to the drop and the power factor matters; Table 9 of the same chapter carries the AC figures and is not reproduced here.
- Three phase assumes a balanced load and gives the drop between lines. A single-phase load taken from one line to neutral of a three-phase supply is a single-phase circuit: choose single phase and the line-to-neutral voltage.
- Aluminum conductors need terminations and devices listed for them; the code does not let dissimilar metals be joined except in a device listed for the purpose. Nothing here checks a termination, a lug or a splice.
- The 3% and 5% figures are suggestions in the code's informational notes rather than requirements, though a local amendment, an equipment maker's instructions or a specification can make a tighter figure binding.
A laydown is a rectangle you never get to use all of
The number everybody starts with is the area divided by the pallet. It is always too high, by a margin that grows the tidier the compound is meant to be, and the gap comes from three separate deductions that get made in the wrong order or not at all.
The first deduction is access, and it is the biggest. A forklift or telehandler needs an aisle it can turn in, not merely pass along, and that aisle comes out of the storage area before anything else. Take a laydown of 24 m by 12 m — 288 m² gross. A single 4 m aisle down its length removes 96 m². Three-quarters of a metre of margin along each long edge, so that a stack is never hard against the fence line, removes another 36 m². What is left to store on is 156 m², which is 54 per cent of what was drawn.
The second deduction is the one the arithmetic cannot see at all: tiling loss. Dividing 156 m² by a 1.2 m² pallet gives 130 positions per layer, and that answer assumes the pallets tessellate the shape perfectly. They do not. Split that remaining width into two 3.25 m bays either side of the aisle, and a 1.2 m by 1.0 m pallet gives three rows across a bay with a quarter of a metre wasted, twenty pallets along the length, sixty per bay — 120 positions, not 130. Eight per cent, on one layer, on a bay that divides neatly. Set the same exercise out on a compound that is a trapezoid because the boundary is, and the loss is worse.
The third is that the two pre-filled dimensions in any capacity tool are the two most likely to be wrong for your material. A footprint of 1.16 m² is often quoted for the North American 48 by 40 in pallet, but that pallet is 13.3 ft², which is 1.24 m²; the 1200 by 800 mm EUR pallet described in EN 13698-1 is 0.96 m², and the 1200 by 1000 mm size in ISO 6780 is 1.20 m². Use the one you will actually receive. And the height field is height per stacked pallet including its load — a bare timber pallet is around 0.14 m, so leaving a default near that value in the field describes a stack of empty pallets and returns a capacity figure that is pure fiction.
- Measure the laydown on the ground after the platform is built, because the stone edge is never where the plan put it.
- Take out the aisle at the width the machine needs to turn, then the edge margins, and store only what is left.
- Set the bays out at the real pallet dimensions and count rows and columns, rather than dividing one area by another.
- Get the loaded height of the units you are storing from the supplier's despatch note, not from the pallet.
- Apply the stacking limit for the material before the height limit of the compound — they are rarely the same number.
- Leave one bay empty from day one, because the first over-delivery arrives before anybody has agreed where to put it.
Run it on the area left after the aisle and the margins are removed, with the loaded pallet height rather than the pallet's own — the two layers of rounding down in it are honest, and they are what make the answer a count rather than an estimate.
The total floor/yard area available for pallet storage.
The floor area occupied by a single pallet.
The maximum allowable stack height (ceiling, rack, or safe-stacking limit).
The height of a single loaded pallet in the stack.
Total pallet storage capacity
320 pallets
This assumes uniform pallet footprint and height with no aisle/access clearance deducted — subtract clearance space for forklift access or walkways from the storage area before using this calculator for a realistic count.
- Pallets per layer
- 16 pallets
- Stack layers
- 20 layers
They open the calculator with your figures already in it
Timber Pallet Stack Storage Capacity Calculator: 320 pallets — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- Divides area by area, which assumes the pallets tessellate perfectly. Floor space is a shape, not a number: a 1.2 x 1.0 m (3.3 ft) pallet has to fit a real bay dimension by dimension, so a strip 2.2 m (7 ft) wide holds one row and wastes the last metre, while the same area in a squarer bay holds two. Set the grid out on the actual bay dimensions before trusting this count - on an awkward footprint the shortfall against the area division is commonly 10 to 20%.
- Counts positions, not weight. Every floor has an allowable uniform load, and it bites hardest on a suspended slab, a mezzanine or a container floor: a full-height block of dense product concentrates a great deal of weight onto each pallet footprint. Multiply pallets per position by the loaded weight and check it against the floor's rating in kPa or psf, because the height limit that governs is often structural rather than the ceiling.
- The safe stack height comes from what is being stacked. Everything above the bottom pallet is carried by the bottom unit load, and corrugated packaging loses a large share of its compression strength over time under load and in humid air, so a block that stands square on day one can lean or crush by week six. Loads with an uneven or non-flat top cannot be block-stacked at all and need racking, which changes the geometry entirely.
The stacking limit is not yours to choose
Height in a laydown is capped by whichever of three limits arrives first, and the one people reach for — the reach of the machine — is usually the last of the three. The material's own stacking rules come first. OSHA 29 CFR 1926.250, General requirements for storage, is explicit about several of them: brick stacks not more than seven feet high, tapered back two inches per foot of height above the four-foot level; masonry block tapered back half a block per tier above six feet; lumber stacked no more than sixteen feet if it is handled manually, and twenty feet if a forklift is used. The same section requires everything stored in tiers to be stacked, racked, blocked, interlocked or otherwise secured against sliding and collapse, and requires aisles and passageways to be kept clear — which is the same aisle you already took out of the area.
The second limit is the platform, and it is a stress rather than a height. A stack of dense material on a small footprint is a bearing pressure problem in exactly the way a cabin jack is, and doubling the height doubles the pressure at the dunnage. Where the material is heavy and the platform was designed for a uniform yard load, the honest move is to spread the footprint rather than to argue with the design. And when the material has been out in the weather, remember that the load includes what has soaked into it: timber, blockwork and bagged product all gain weight through a wet fortnight, and packaging that has slumped is also packaging that has stopped bearing evenly.
The parts of the compound that are somebody's legal entitlement
Welfare is not a layout preference. In Britain the Construction (Design and Management) Regulations 2015 set out in Schedule 2 what has to be provided — sanitary conveniences, washing facilities, drinking water, changing rooms and lockers, and a rest facility with the means to prepare a hot drink and heat food — and the duty is to have it from the start of the work, not from whenever the second delivery of cabins lands. In the United States the equivalent obligations are in OSHA 29 CFR 1926.51, Sanitation, which sets toilet provision against headcount in its own table and covers potable water and washing facilities. Both are sized off peak headcount, and peak headcount is a programme output that somebody has to go and get.
That obligation is what actually sets the compound's footprint on most jobs, and it is why the laydown ends up as the residual rectangle. Work the cabin schedule from the headcount curve first, place the welfare units where the walk from the work face is short enough that people use them, and treat what is left as the storage area — rather than laying out storage and fitting welfare into the corner, which is the order that produces a compound people quietly stop using.
Fire and escape run through all of it. NFPA 241, Standard for Safeguarding Construction, Alteration, and Demolition Operations, requires a fire prevention programme for the site, and a compound of stacked combustible material next to occupied cabins is one of the arrangements it exists to catch. Separation between cabin groups, escape routes from the far end of a stack of units, an assembly point that is not inside the compound, and vehicle access kept open to the cabins are all layout decisions rather than paperwork, and every one of them is cheaper to make on the plan than after the units are craned in.
Reconcile it at week twelve, when it has stopped being what you built
Compounds drift in one direction only. The laydown fills, the aisle narrows because one delivery was put down in it and never moved, a second row of cabins arrives when the headcount curve turns out steeper than the programme said, and the temporary supply that was sized for one office is now feeding two, a welding set and a canteen microwave. None of that gets noticed until something trips or somebody cannot get a forklift down the middle.
The reconciliation is cheap and worth booking. Walk the aisle with a tape and see whether it is still the width the machine needs. Count what is actually stacked against what the capacity exercise said would fit, because a consistent gap in one direction means the loaded height or the tiling assumption was wrong and both are worth correcting before the next phase's material arrives. Add up what has been plugged in since the supply was commissioned and re-run the connected load; if it has moved past what the head was sized for, that is a conversation with the electrician now rather than an outage in the middle of a pour. Then check the platform where the wheels turn, because that is where it fails first, and a rut that has started to hold water in week twelve is a repair, while the same rut in week thirty is a rebuild with everything standing on it.
Settle these before the cabins are craned in
Six figures that decide whether the compound works, each of which is fixed at the moment something heavy is put down on it and expensive to change afterwards.
- Peak headcount off the programme curve — It sizes the welfare schedule, which sizes the cabin stack, which is what the laydown gets the remainder of. Take it from the resource curve, not from the first month.
- Winter connected load, cabin by cabin — Nameplates for lighting, heating and cooling, and receptacle equipment, entered per cabin and summed — with the fan heaters that appear in November counted in.
- Walked distance from the head to each cabin — The route the cable takes round the laydown, not the straight line. It sets the conductor size long before ampacity does.
- Designed platform thickness and the area it covers — Thickness comes from a designer working off a measured subgrade strength; the area comes off the ground after setting out. The tonnage follows from the pair.
- Storage area after the aisle and margins are removed — Gross rectangle less the turning aisle less the edge setback, then bays counted out at real pallet dimensions rather than divided as an area.
- Loaded stack height and the limit that caps it — Material stacking rules first, platform bearing second, machine reach last — and the loaded pallet height from the despatch note, never the bare pallet.
Opens the calculators above on one screen with the dimensions from this article already filled in. Quantities only — this site publishes no price list, because local prices vary too much to publish honestly.