Craft QuantitiesMethods and verification
This site publishes several hundred calculators, and they are not several hundred different methods. They are about a dozen, applied to different materials and markets.
These papers write those methods out in full — the equations, what each symbol means, and, more usefully, where the method stops being reliable. The point is that you should not have to trust any individual page: if you understand why a material count is a ceiling function, or why a column form sees higher pressure than a wall form of the same height, you can check any calculator built on that method against your own arithmetic.
Every equation is real MathML rather than an image, so it scales with your font size, can be selected and copied, and is read correctly aloud.
Turning a measurement into an order. This shelf sits behind more of the registry than the rest combined, and the arithmetic is deliberately the least interesting part — the risk lives in the waste factor and the rounding, not in the division.
Why a material count is a ceiling function rather than a division, and why the waste factor — not the geometry — carries the risk.
Runs behindAAC Block Thin-Bed Mortar Calculator, Air Barrier Sealant Tape Linear Footage Calculator, Cleanroom Air Shower Nozzle Count Calculator and 131 more
3 sections · 134 calculators
Converting a plan footprint into the sloped area a roof actually has — the factor that decides whether a shingle order is right or a third short.
Runs behindSolar Array Row Spacing and Shading Pitch Calculator, Roof Squares Calculator, Roof Pitch to Angle Calculator and 19 more
8 sections · 22 calculators
Why sheet and length counts are a packing problem, why kerf is charged per cut, and why the optimiser is a heuristic rather than an optimum.
Runs behindPlaster Angle and Stop Bead Calculator, Tiled Stair Calculator, Lineal Timber Cut List Calculator (Posts and Beams from Stock Lengths)
6 sections · 3 calculators
How a datasheet figure becomes an order quantity, why it is quoted per coat and calculated for a smooth plane, and what a real substrate does to it.
Runs behindWet Room Tanking and Waterproof Membrane Calculator, Asphalt Crack Filler Calculator, Asphalt Emulsion Prime Coat Calculator and 40 more
5 sections · 43 calculators
Why most conversion factors carry no uncertainty at all, which ones hide a material assumption, and why converting a measurement can never make it more precise than it was.
Runs behindAcres to Hectares Calculator, Acres to Square Feet Calculator, Amps to Watts Calculator (120 V) and 190 more
6 sections · 193 calculators
Why a run divided by a spacing gives the number of gaps and not the number of things, why the division rounds up rather than to nearest, and what the leftover bay at the end does to both.
Runs behindBaseplate Anchor Bolt Pattern Layout Calculator, Brick Veneer Anchor Spacing Calculator, Ceiling Joist Spanning Lineal Lumber Aggregator and 39 more
5 sections · 42 calculators
Why the depth carries almost all the risk in a volume, why an excavation holds far more than its plan area suggests, and why a bag's yield is not its weight divided by a density.
Runs behindAsphalt Driveway Calculator, Column Pier Size from Baseplate Edge Distance Calculator, CMU Cell Grout Volume Calculator and 49 more
6 sections · 52 calculators
Why a rolled steel section's mass is read from a table rather than computed, why one material has five densities, and why a tonne of wet sand is less sand.
Runs behindAquarium Display Tank Water Weight Calculator, Architectural Glass Weight Calculator, Boulder Weight Range Calculator and 33 more
6 sections · 36 calculators
Why covering an area with rolls is a strip count rather than a division, why the lap is bought twice over, and why turning the strips the other way can change the order.
Runs behindArtificial Grass and Synthetic Turf Calculator, Attic Radiant Barrier Calculator, Board and Batten Siding Calculator and 31 more
6 sections · 34 calculators
Why a sloping run exceeds its plan projection, why a bend is SHORTER than the square corner it replaces, and why an equivalent length is not a length you can order.
Runs behindCommercial ADA Accessible Ramp Length & Landing Calculator, EMT Conduit Bend Length Calculator, Cone and Frustum Flat Pattern Development Calculator and 11 more
6 sections · 14 calculators
Why a hundred cubic metres dug out becomes a hundred and twenty-five to cart away and ninety when it is put back, and why a cut-and-fill balance struck in the wrong state does not balance.
Runs behindBackfill Compaction Lift Count Calculator, Debris Container Fill Efficiency Calculator, Slope Cut-and-Fill Earthwork Balance Calculator and 8 more
6 sections · 11 calculators
Why a litre of water added on site costs strength permanently, why yield is the sum of absolute volumes rather than of loose ones, and why strength is a function of temperature and time together rather than of age.
Runs behindACI 211.1 Water-Cement Ratio Calculator, Aggregate Fineness Modulus Calculator (ASTM C136), Concrete Aggregate Moisture Correction Calculator and 14 more
6 sections · 17 calculators
Why Approved Document M ties a ramp's gradient to its length, why a ramp over 300 mm needs steps beside it and one over 2 m a lift, why a door's width is not its leaf, and why an external step has a range rather than a figure.
Runs behindAccessible Ramp Flights and Landings Calculator (Approved Document M), Door Effective Clear Width Calculator (Approved Document M and ADA), External Stepped Access Calculator (Approved Document M)
5 sections · 3 calculators
Why you choose the number of risers rather than their height, why the spread across a whole flight is held to three-eighths of an inch, and why a cable railing has to be checked deflected rather than at rest.
Runs behindADA Ramp Handrail Extension Calculator, Deck Baluster Calculator, Cable Railing Calculator and 9 more
8 sections · 12 calculators
Why a fixing count is never area divided by spacing, why the edges of a panel supply more fasteners than its middle, and why the tighter schedule at a roof corner is a requirement rather than caution.
Runs behindRaised Access Floor Panel and Border Count Calculator, Raised Access Floor Pedestal Count Calculator, Raised Access Floor Stringer Bar Calculator and 24 more
7 sections · 27 calculators
Why a room's area tells you nothing about how much skirting it needs, why adding a door can increase the trim order, and why a crown moulding mitre is neither forty-five degrees nor half the corner angle.
Runs behindBaseboard & Trim Calculator, Cavity Barrier Run and Crossing Count Calculator, Drop-Ceiling Main Runner Splice Calculator and 31 more
7 sections · 34 calculators
Why an accessible dimension is a measured anthropometric result rather than a round number, why a parking layout is set by the vehicle that turns worst, and why a door needs floor space on the side nobody draws.
Runs behindAccessible Parking Space Count Calculator, Security Bollard Spacing Calculator, Pedestrian Covered Walkway Support Bay Spacing Calculator and 17 more
8 sections · 20 calculators
Why a sealant twice as deep is worse rather than better, why three-sided adhesion destroys a joint that never saw its rated movement, and why a firestop is a tested assembly rather than a tube of product.
Runs behindFiber-Cement Siding Caulk Joint Volume Calculator, Firestop Joint Movement and Sealant Volume Calculator, Penetration Firestop Caulk Volume Calculator and 3 more
6 sections · 6 calculators
Why a two-by-four is one and a half by three and a half, why a board foot is a volume the board does not contain, and why checking the diagonals finds an error that measuring the sides cannot.
Runs behindAcreage Calculator, Arc Chord and Mid-Ordinate Check Calculator, Board Feet Calculator and 11 more
6 sections · 14 calculators
Why a brick's working size is the unit plus its joint, why a dry brick ruins the mortar bond, and why a veneer's shelf angle is governed by eccentricity rather than by weight.
Runs behindRadial Arch Brick Wedge Taper Calculator, Ashlar Stone Masonry Joint Volumetrics Calculator, Brick Initial Rate of Absorption (IRA) Calculator and 7 more
7 sections · 10 calculators
Why a raised floor is designed for one wheel rather than for a crowd, why a small opening is deliberately not deducted, and why a cutout costs more than the area it removes.
Runs behindElectric Underfloor Heating Mat Area Calculator, Access Floor Cable Cutout Area Calculator, Raised Access Floor Rolling Load Check Calculator and 3 more
5 sections · 6 calculators
Something moving through something, or heat leaving. A duct, a drain and a pool turnover are the same problem with different fluids and different tolerances for getting it wrong.
The single equation behind water heater sizing, duct heating and every temperature-rise problem on the site.
Runs behindTankless Water Heater Sizing Calculator, Water Heater Sizing Calculator, Solar Water Heater Collector Size Calculator and 6 more
6 sections · 9 calculators
Why R-values add but U-values do not, and why the assembly you build never performs like the assembly you specified.
Runs behindAttic Insulation Upgrade Calculator, Continuous Insulation Thermal Bridging Calculator (Z-Furring), Insulation R-Value by Climate Zone Calculator (IECC 2021 and NBC 2020) and 10 more
8 sections · 13 calculators
Why sizing a conduit is really choosing a velocity — capped above by noise and wear, held up from below by settlement — and then solving for the area.
Runs behindDuct Air Velocity Calculator, Duct Size Calculator, HVAC Duct Size Calculator and 6 more
5 sections · 9 calculators
One inferred number — the water volume — sets the chemical dose, the pump flow and the heater, and nobody ever measures it directly.
Runs behindPool Total Alkalinity Adjustment Calculator, Pool Filter Backwash Water Calculator, Pool Calcium Hardness Increaser Calculator and 11 more
7 sections · 14 calculators
Why glass has no strength until you say how long the load lasts, why the edge of a sealed unit leaks more heat than the middle, and why a mullion's deflection limit protects the seal rather than the glass.
Runs behindAcoustic Laminated Glass STC Rating Estimator, Blast-Resistant Fenestration Rating Checker, Curtain Wall Spandrel Condensation Risk Checker and 17 more
7 sections · 20 calculators
Why a wooden louvre delivers a quarter of the hole you cut and a metal one three-quarters, why intake and exhaust have to be balanced or the roof ventilates the house, and why doubling the pressure does not double the flow.
Runs behindBathroom Extract Fan Rate and Duct Resistance Calculator, Attic Rafter Baffle/Chute Count Calculator, Attic Baffle Vent Calculator and 9 more
6 sections · 12 calculators
Why one pipe size up cuts the friction to a third, why a compressed flex duct can cost four times its rated loss, why a drain can be too steep, and why a fast-closing valve produces a pressure the pump never could.
Runs behindHydronic Circulator Pump Head Loss Calculator, Drain Pipe Slope Calculator, Duct Design Friction Rate Calculator (ACCA Manual D) and 19 more
8 sections · 22 calculators
Why a blower-door result is not an air change rate, why a leak at the top of a house matters far more than the same leak halfway up, and why sealing without ventilating moves the problem rather than solving it.
Runs behindAir Changes Per Hour (ACH50) Calculator, Air Permeability (q50) and Test Flow Calculator, Attic Bypass Sealing Material Calculator and 6 more
7 sections · 9 calculators
Why an expansion vessel is two to three times bigger than the water it has to absorb, why makeup water is a fault report rather than a consumable, and why a refrigerant line that is too large starves its own compressor of oil.
Runs behindBoiler Makeup Water Calculator, Thermal Expansion Tank Sizing Calculator, Dielectric Union Galvanic Corrosion Risk Evaluator and 7 more
7 sections · 10 calculators
Why a hundred fixtures do not need a hundred times one fixture's flow, why low-flow fittings turned an oversized water main into a health problem, and why a grease interceptor is sized on time rather than on flow.
Runs behindDomestic Hot Water Recirculation Flow Calculator, Grease Trap Sizing Calculator (PDI-G101 Method), Septic Tank Sizing Calculator and 3 more
6 sections · 6 calculators
Why two houses of identical floor area can need three times different capacity, why an oversized air conditioner leaves a room clammy, and why a radiator that suited a boiler is too small for a heat pump.
Runs behindAir Conditioner Size Calculator, Electric Baseboard Heater Sizing Calculator, Baseboard Heater Length Calculator and 9 more
8 sections · 12 calculators
Why a leaky asbestos enclosure needs more air rather than less, why an island cooker hood needs far more than a wall one, and why a powered attic fan can pull conditioned air out of the house it is cooling.
Runs behindAsbestos Enclosure Negative-Pressure Airflow Calculator, Attic Fan CFM Calculator, Cleanroom HEPA Airflow & Face Velocity Calculator and 3 more
6 sections · 6 calculators
Why a lightly loaded generator wastes fuel and damages itself, why a propane tank can be full and still starve an appliance in cold weather, and why a bigger softener uses less salt per litre treated.
Runs behindCompost Blend Calculator, Concrete Washout Basin Solidifier Dosage Calculator, Generator Fuel Runtime Calculator and 6 more
6 sections · 9 calculators
Energy that adds logarithmically, so the weakest path decides the outcome. Almost every disappointing result in this group is a small gap or a rigid bridge rather than the wrong material.
Why one per cent of open area destroys an otherwise excellent wall, why doubling the mass buys only six decibels, and why an isolator with too little deflection makes vibration worse rather than better.
Runs behindAcoustic Ceiling Cloud Suspension Wire Count Calculator, Acoustic Laminated Glass STC Rating Estimator, Acoustic Reflector Panel Placement Calculator and 7 more
8 sections · 10 calculators
Why an hour at 94 dB(A) is a whole day at 85, why two countries' rules disagree about the same shift, why twice the vibration is four times the dose, and why a protector rated 30 dB takes off far less.
Runs behindConstruction Plant Noise at a Neighbour Calculator (BS 5228-1 / FHWA RCNM), Daily Noise Exposure (LEP,d) Calculator, Decibel Addition and Background Correction Calculator and 7 more
9 sections · 10 calculators
Force, and what geometry and repetition do to it. The recurring shape is a demand that grows faster than the input causing it — squared, cubed, or to the fourth power — which is why intuition is a poor guide here.
Why a pavement is designed around the few percent of traffic that is heavy, and cars are almost irrelevant to it.
Runs behindFlexible Pavement AASHTO Structural Number (SN) Calculator, Pavement Design ESAL Calculator
6 sections · 2 calculators
Why a column form sees full hydrostatic pressure and a wall form usually does not, and why temperature belongs in the equation.
Runs behindACI 347 Column Formwork Pressure Calculator, ACI 347 Wall Formwork Rate-of-Placement Pressure Calculator, SCC Formwork Lateral Pressure Calculator and 2 more
7 sections · 5 calculators
Why a restrained element's stress is the same whatever its length, why a clay brick outer leaf and a block inner leaf move in opposite directions, and why a joint's width is set by the sealant rather than by the movement.
Runs behindDrywall Ceiling Control Joint Spacing Calculator, Concrete Control Joint Spacing Calculator, Firebrick Chimney Liner Thermal Expansion Calculator and 12 more
6 sections · 15 calculators
Why anchorage length scales with bar diameter rather than area, why bond actually fails by splitting the cover rather than by sliding, and why a lap is longer than a development length.
Runs behindPost-Tensioned Anchor Seating Loss Calculator, Rebar Development Length Calculator (ACI 318), Rebar Lap Splice Length Calculator (ACI 318) and 1 more
7 sections · 4 calculators
Why an anchor's capacity is the smallest of several modes rather than one number, why concrete breakout grows with embedment to the power of one and a half, and why hole cleaning is the largest variable on site.
Runs behindConcrete Anchor Bolt Breakout Capacity Calculator (ACI 318), Concrete Anchor Proof Load Test Calculator, Bolt Group Shear, Bearing and Tearout Calculator and 11 more
6 sections · 14 calculators
Why depth is worth four times what width is in bending, why reinforced concrete is deliberately designed to fail in the steel rather than the concrete, and why a notch removes far more strength than material.
Runs behindBeam and Joist Point Load Moment Calculator (Equivalent UDL), Castellated Beam Web Opening Net-Section Shear Calculator, Concrete-Filled HSS Composite Column Capacity Calculator and 10 more
6 sections · 13 calculators
Why doubling a span multiplies its deflection by sixteen, why a stronger grade of steel does nothing for it, and why a floor that passes every deflection check can still be unacceptable to walk on.
Runs behindCold-Formed Steel (CFS) C-Stud Deflection Checker, Corrugated Metal Decking Span Deflection Checker, Floor Beam Vibration Natural Frequency Calculator and 6 more
6 sections · 9 calculators
Why the ends of a column matter more than its material, why a flat arch thrusts so much harder than a deep one, and why height-to-thickness rules exist at all.
Runs behindBrick Arch Rise-to-Span Ratio Calculator, Masonry Prism Height-to-Thickness Ratio Validity Checker, Masonry Parapet Height-to-Thickness Ratio Calculator and 2 more
5 sections · 5 calculators
Why a scaffold must be tied once it stands four times as tall as it is wide, why a duty rating is an average a pallet of blocks ignores, and why half an inch more plank thickness more than doubles its stiffness.
Runs behindScaffold Plank Span Calculator (OSHA Appendix A), Scaffold Platform Load and Duty Rating Calculator, Scaffold Tie Count Calculator (OSHA 1926.451)
5 sections · 3 calculators
Why a shallow sling angle doubles the tension in every leg, why a sheeted scaffold carries an order more wind than an open one, and why adding trucks to a short haul achieves nothing.
Runs behindCrane Lift Utilisation Calculator, Suspended Load Wind Force and Swing Calculator, High-Rise Debris Drop Chute Impact Energy Calculator and 9 more
7 sections · 12 calculators
Why a warm sheltered roof carries more snow than an exposed cold one, why building next to an existing low roof can overload it without touching it, and why a collar tie and a rafter tie are not the same member.
Runs behindCollar Tie Wind Uplift Tension Calculator, Ridge Beam Tributary Load Calculator, Roof Snow Drift Surcharge Calculator and 4 more
6 sections · 7 calculators
Why the same joist is stronger against a wind gust than against a bookcase, why a notch is limited by geometry rather than by stress, and why a heavy timber beam can outlast an unprotected steel one in a fire.
Runs behindCLT Floor Panel Grid Layer Calculator, Deck Joist Span and Size Calculator, Shed Foundation Skid Calculator and 3 more
7 sections · 6 calculators
Soil and the water in it, where the governing parameters vary more than anywhere else on this site and what a site carried in the past matters as much as what you are about to add. Every paper here ends at the point a ground investigation has to take over.
Why one soil has three pressures that differ ninefold, why the resultant acts a third of the way up rather than halfway, and why water is what actually fails retaining walls.
Runs behindRankine Active Earth Pressure with Surcharge Calculator, Basement Wall At-Rest Earth Pressure Calculator (with Groundwater), Excavation Bracing Strut Load Calculator and 6 more
5 sections · 9 calculators
Why the allowable pressure under a footing is usually set by settlement rather than by strength, why a wider footing settles more at the same pressure, and why timber bearing is limited by the weakest direction of the grain.
Runs behindCrane Outrigger/Mat Ground-Bearing Pressure Calculator, Footing Soil Bearing Pressure Checker, I-Joist Web Stiffener Bearing Length Calculator and 7 more
6 sections · 10 calculators
Why shaft friction and end bearing cannot simply be added at working load, why settling ground turns friction from a resistance into a load, and why ten piles do not carry ten times what one does.
Runs behindDriven Pile Skin Friction Capacity Calculator (Alpha Method), Negative Skin Friction (Downdrag) Calculator, Pier Adfreeze Uplift Calculator and 4 more
5 sections · 7 calculators
Why permeability varies over ten orders of magnitude and therefore dominates every seepage answer, why the radius of influence is an empirical fudge rather than a measurement, and why dewatering settles the neighbours.
Runs behindDarcy's Law Seepage Flow Rate Calculator, Dewatering Well Yield Calculator (Dupuit-Forchheimer), Pump Drain Time Calculator and 2 more
5 sections · 5 calculators
Why 95% compaction is not a number until you name the test, why what a site was loaded with in the past matters more than what you are about to put on it, and why seepage roughly halves a slope's factor of safety.
Runs behindBentonite Waterproofing Swell Thickness Calculator, Primary Consolidation Settlement Calculator, Infinite Slope Stability Factor of Safety Calculator and 5 more
7 sections · 8 calculators
Why a pavement's thickness is decided by the ground rather than by the traffic, why an SPT blow count read straight off a log is systematically wrong, and why a flexible culvert is really a soil structure.
Runs behindRigid Airfield Pavement Edge Stress Screening Calculator, Asphalt In-Place Density (Percent of Gmm) Calculator, Roadway Base Course Aggregate Tonnage Calculator and 4 more
7 sections · 7 calculators
What a building emits, and what it does with the rain that lands on it. The arithmetic in this group is a multiplication; the difficulty is entirely in the boundary, and a figure here means nothing until you say what it includes and what it leaves out.
Why two embodied carbon figures for the same product can differ by a factor and both be right, why a low-cement mix is partly an accounting decision, and why multiplying today's grid factor by thirty years overstates the answer.
Runs behindC&D Debris Recycling Diversion Rate Calculator, Structural Material Carbon Comparison Calculator, Embodied Carbon in Concrete Calculator and 3 more
7 sections · 6 calculators
Why a small catchment is designed for a more intense rainfall than a large one, why a detention basin can make things worse downstream, and why a rainwater tank delivers far less than annual rainfall times roof area.
Runs behindGrassed Swale Capacity & Velocity Calculator, Green Roof Vegetated Tray Rainwater Retention Calculator, Greywater Collection Cistern Peak Inflow Calculator and 10 more
9 sections · 13 calculators
Conductors, faults and stored charge. Sizing problems where the nameplate figure is not the usable one, and where the safe answer depends on how fast something disconnects rather than only on how much current is available.
The two multiplications that separate a battery's nameplate from what it will actually run — commonly a factor of two and a half.
Runs behindBattery Bank Sizing Calculator, Off-Grid Autonomy Calculator, Battery Backup Runtime Calculator
6 sections · 3 calculators
Why the run length doubles, why a 12 V circuit suffers a hundred times the percentage loss of a 120 V one, and why ampacity answers a different question entirely.
Runs behindWire Gauge Voltage Drop Calculator (Copper or Aluminum, AWG to 1,000 kcmil), Extension Cord Gauge Calculator, Landscape Lighting Wire Calculator and 6 more
5 sections · 9 calculators
Why a ground rod cannot clear a fault, why doubling a rod's diameter achieves almost nothing, and why a LOWER available fault current can produce a more dangerous arc flash.
Runs behindBusbar Ampacity Calculator (Current Density Method), Electrical Equipment Working Clearance Space Calculator, Isolated Ground Rod Earth Resistance Calculator (Dwight's Formula) and 4 more
7 sections · 7 calculators
Why the sum of every nameplate is a load no building ever draws, why a motor's conductors are sized from a table rather than from its nameplate, and why a dark room needs far more light than a pale one for the same lux.
Runs behindBreaker Size Calculator, Electrical Circuit Load Calculator, Electrical Panel Load Calculator (NEC Service Sizing) and 17 more
8 sections · 20 calculators
Why a conduit is full at forty per cent, why two ninety-degree bends can multiply a pull force fivefold, and why snow melting needs far more power per square metre than heating the space above it.
Runs behindElectrical Box Fill Calculator (NEC 314.16, US), Cable Tray Center-Span Deflection Calculator, Cable Tray Fill Percentage Calculator and 6 more
7 sections · 9 calculators
Why a solar string is limited by the coldest morning rather than the hottest day, why an array deliberately exceeds its inverter's rating, and why a small shadow can suppress a whole string.
Runs behindSolar Inverter Sizing Calculator, LED Strip Power Supply Calculator, Ohm's Law Calculator and 4 more
6 sections · 7 calculators
Cash over time. Tax bands, loan amortisation and earned value all work by slicing a total into pieces that are each treated differently — the shape that makes marginal and average rates diverge.
Why crossing a stamp duty threshold does not reprice the whole purchase, and where a genuine cliff does exist.
Runs behindUK Stamp Duty (SDLT) Calculator, Ontario Land Transfer Tax Calculator
7 sections · 2 calculators
The annuity formula behind every repayment figure, and why the zero-rate case needs its own branch.
Runs behindMortgage Payment Calculator, Mortgage Affordability Calculator, Home Improvement Loan Payment Calculator
7 sections · 3 calculators
How three numbers become a forecast, why the schedule index lies at the end of a project, and what TCPI is really asking.
Runs behindEarned Value Management (EVM) Calculator
8 sections · 1 calculators
Why a duration is only as good as its output rate, why the critical path is the longest chain rather than the busiest, why twenty working days is four weeks, and why a repeated task gets faster by doublings.
Runs behindActivity Duration and Crew Size Calculator, Critical Path and Float Calculator (CPM), Repetition Learning Curve Calculator (Wright and Crawford) and 1 more
5 sections · 4 calculators
Why a 20% markup is not a 20% margin, why an estimate without a range is the wrong shape of answer, and why contingency should shrink as a design develops rather than staying at ten per cent forever.
Runs behindBathroom Remodel Cost Calculator, Board Foot Lumber Cost Calculator, Contractor Markup Calculator and 14 more
7 sections · 17 calculators
Why simple payback is the weakest measure in common use, why two options with different lifespans cannot be compared on total cost, and why recouping 70% of a renovation at resale is a loss rather than a return.
Runs behindAppliance Energy Cost Calculator, Equipment Rental vs. Buy Calculator, EV Home Charging Cost Calculator and 11 more
7 sections · 14 calculators
Why a contractor finances the retention on every project, why a change costs far more late than early, and why a skip that looks half empty can already be over its weight limit.
Runs behindChange Order Cost Calculator, Delay Cost and Acceleration Break-Even Calculator, Dumpster/Skip Container Size Selector and 5 more
7 sections · 8 calculators
Not a domain but a technique the others borrow: what to do when an equation is easy to evaluate forwards and impossible to rearrange backwards.
How the site inverts any calculator — and why bisection rather than Newton–Raphson is the correct choice here.
7 sections
Take the result you were given, find the paper the calculator is built on, and reproduce the number by hand from the equation. If it agrees, you have verified the page rather than believed it. If it disagrees, one of two things is true — the calculator applies a refinement the paper simplifies away, or the calculator is wrong — and both are worth knowing before the material is ordered.
Each paper ends with where its method stops being reliable, which is the part that matters on site. A coverage rate assumes a surface with a particular porosity; a thermal-resistance sum assumes the layers are actually continuous; a slope factor assumes the plane is planar. Those assumptions fail in ordinary buildings, and the paper says so rather than leaving you to discover it.
The calculators apply these methods to specific materials, the trade guides cover the site work the arithmetic cannot describe, and the comparisons handle the decisions that come before any of it. Whether each calculator still returns the figures its sources give is checked by the published test cases, run on every push.