Laying a Gravel Driveway

What this calculation does not cover

• Fills the truck by VOLUME, and a haul truck usually fills by WEIGHT first. Payload is loose volume x loose density, and excavated wet clay at roughly 1.6 t/m³ (about 2,700 lb/yd³) puts 19 tonnes (21 tons) in a 12 m³ (16 yd³) box — past the legal axle load long before the material reaches the top of the sides. On heavy or saturated material the trip count comes off the truck's rated payload in tonnes, and this figure will be optimistic.
• Takes the rated bed capacity at face value. A heaped rating only holds for material that will stand in a heap: wet, sticky subgrade sheds off the sides, has to be sheeted, and leaves a skin in the box on every tip, so the volume actually moved per trip is nearer the struck capacity. Enter the struck figure for anything that will not heap.

What this calculation does not cover

• Length × width × depth is a single rectangle at a single thickness, so a drive that curves, splays at the entrance or opens out into a parking bay has to be measured as several rectangles and the answers added, and nothing is deducted for a manhole, a kerb line or a planted island sitting inside the area.
• That thickness is then spread evenly over the whole footprint, which assumes ground already graded true — ruts, hollows and the first load that disappears into a soft patch are material the product of three numbers cannot see, and there is no separate term for a levelling course under the stone.
• The compaction allowance is one flat percentage of the finished volume, applied to the whole job at once and stopping at 40%, rather than a figure derived from the grading or the moisture of what you are actually buying; it is also added to the finished volume rather than divided out of it, so 20% here means 1.20 times the finished figure, not the 1.25 that losing a fifth of a loose load to settlement would call for.
• The weight and the loose volume are the same load: the tonnage is the loose volume to order, compaction allowance included, at one fixed loose bulk density of 1600 kg/m³ (100 pcf), with no field to change it. That suits stone delivered loose and spread or lightly rolled; a dense-graded base (crusher run, DGA, Type 1) specified by its compacted thickness weighs about 2200 kg/m³ (137 pcf) in place and is better worked on the gravel base tonnage page, which takes a compacted density.
• Nothing in the arithmetic asks what will drive over the surface or what lies beneath it: any depth from 10 mm (0.39 in) to a metre is accepted without a check on wheel loads or subgrade strength, and a build that puts a coarse base course under a finer wearing course is two separate runs of this page rather than one.
• What comes back is an exact arithmetic tonnage, not an order quantity — it is not rounded up to whole bulk bags, to the minimum load a tipper will bring out, or to the increment your yard sells in, so the last step of rounding upward is yours once you know how the material is sold.

What this calculation does not cover

• Covers the neat prism only, area times depth. A base course is normally laid wider than the surfacing it carries, running past the edge of asphalt and then falling away on a batter, and that widening is real tonnage — take the area off the paved width alone and the order is short by the shoulder on every load.
• The density asked for is the compacted in-place figure; the ticket at the weighbridge is wet weight. Aggregate leaves the pit carrying free moisture, a few percent by mass in normal weather and appreciably more after rain, so the mass bought and the mass placed are two different numbers and the difference is water you paid for.
• Nothing here allows for stone lost into the subgrade. A soft or pumping formation swallows part of the first lift as the roller works it, and the material that disappears below the design line still came off a truck — on weak ground the order needs an over-excavation allowance, or a separation geotextile to stop the loss.

What this calculation does not cover

• There is no moisture input. Both boxes take dry density, and nothing here checks the placement-moisture band that specifications normally pair with the density clause, so a lift can hit the percentage while being placed too dry or too wet of optimum. Enter a wet gauge reading in the field box by mistake and the percentage comes out inflated with no warning.
• The page assumes both densities are on the same basis and does not verify it. It has no way to know whether the laboratory maximum came from a Standard or a Modified Proctor, or whether that curve was run on the material actually in this lift rather than carried over from an earlier borrow face.
• No oversize correction is applied. A Proctor is run on screened material with the large particles taken out, so a gravelly or coarse fill can measure denser in the field than that curve suggests and read at or above 100% while still short of the compaction the specification intends.
• The percentage describes one test at one spot, to the depth that gauge or sand cone reaches. It carries no testing frequency, no lot size, and no view of whether acceptance rests on every individual test or on the average of a set with a floor under any single result.
• Both density boxes are limited to roughly 1,000-2,500 kg/m³ (about 62-156 pcf), and a value outside that is replaced by the nearest bound before the percentage is worked out. Lightweight aggregate and other low-density fills sit below the floor. The comparison shown is the arithmetic on the three numbers you typed, not an acceptance decision and not a check of bearing capacity, settlement or stability; where the fill carries a footing, slab, pavement or retaining structure that call belongs to the geotechnical engineer of record.

What this calculation does not cover

• GRAVEL IS A SURFACE THAT MOVES, and that is the difference between ordering it once and maintaining it. Loose stone migrates to the edges and into ruts under turning traffic, so a gravel drive needs topping up on a cycle that no initial quantity predicts.
• The 1.4 tons (1.3 tonnes) per cubic yard is the weight of crushed stone as tipped or laid loose, not rolled. Stone that is compacted after spreading packs more weight into the same depth.
• Angularity decides whether it stays put. Rounded river gravel rolls under load and never locks; crushed angular stone keys together and holds. Both are sold as 'gravel' at a similar density, and only one makes a driveway.
• Nothing here about a separation layer. Without a geotextile between stone and subgrade, fine soil pumps up into the stone under traffic and the layer loses its structure — which is a failure of specification, not of quantity.
• Tonnage comes from one fixed density, 1.4 tons (1.3 tonnes) per cubic yard, held constant for whatever stone you actually order; pea gravel, crusher run and washed stone do not all weigh the same per yard, and there is no field here to enter the density your quarry quotes.
• Area is length times width, so the shape being priced is a plain rectangle: a flare at the road, a bend, a turning head or a parking bay has to be measured as its own rectangle and the tonnages added together.
• One depth produces one order, but the three-course build described in the questions below - coarse base stone, a mid layer that locks it, then crushed fines on top - is three deliveries of three different sizes, and dividing the total depth between them is left to you.
• The depth is filled at that loose weight with no compaction allowance, so the answer suits a surface course spread and left loose. A layer rolled down to the depth asked for needs more stone than this, and a rolled dense-graded base (crusher run, DGA, Type 1) weighs about 1.85 tons (1.68 tonnes) per cubic yard in place, which belongs on the gravel base tonnage page. Nothing is added for what beds down into soft subsoil or spills past an unedged verge.
• Gravel depth is the stone layer alone: it is not a dig depth, and no excavation, topsoil-strip or spoil-removal volume falls out of the calculation.
• The result is the exact fraction of a ton the arithmetic produces, while stone is delivered in whole loads and most suppliers set a minimum order, so the number to phone through is this one rounded up to what a truck will actually bring.

What this calculation does not cover

• The edge drop is worked as one straight gradient from crown to edge, so where a crown is built as a curve rather than two flat planes only the edge point matches — the pavement at intermediate offsets sits higher, with less drop, than a straight interpolation implies.
• A single half-width and a single cross-slope stand in for both sides of the road, so an asymmetric crown, a widened lane, or a different slope left and right has to be run twice and the two drops read separately.
• Longitudinal grade is absent from the arithmetic: where the road also falls along its length, water leaves the surface on a diagonal path and the true surface gradient is the resultant of the two slopes rather than the cross-slope alone.
• The cross-slope field accepts 1% to 4% only, so a superelevated curve banked beyond that band, or a deliberately flatter section, cannot be entered here.
• Half-width is read as a horizontal plan distance, so a width tape-measured along the crowned surface instead of taken off the drawing is fractionally long and inflates the drop by a correspondingly small amount.
• The figure describes the finished pavement surface between centreline and edge of pavement — course thicknesses, subgrade profile, and any gutter pan or shoulder break beyond that edge sit outside it.