Methodology & Verification
This site publishes several hundred calculators, and they are not several hundred different methods. They are about a dozen methods applied to different materials and different markets. These pages 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 here is real MathML rather than an image, so it scales with your font size and can be read aloud.
Quantity, Waste and Rounding
Why a material count is a ceiling function rather than a division, and why the waste factor — not the geometry — carries the risk.
3 sections · 4 calculators
Slope, Pitch and True Surface Area
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.
3 sections · 4 calculators
Progressive Slice Taxation
Why crossing a stamp duty threshold does not reprice the whole purchase, and where a genuine cliff does exist.
3 sections · 2 calculators
Loan Amortisation
The annuity formula behind every repayment figure, and why the zero-rate case needs its own branch.
3 sections · 3 calculators
Sensible Heat and Flow
The single equation behind water heater sizing, duct heating and every temperature-rise problem on the site.
3 sections · 3 calculators
Thermal Resistance in Series
Why R-values add but U-values do not, and why the assembly you build never performs like the assembly you specified.
3 sections · 3 calculators
Usable Battery Energy
The two multiplications that separate a battery's nameplate from what it will actually run — commonly a factor of two and a half.
3 sections · 3 calculators
Fourth-Power Load Equivalency
Why a pavement is designed around the few percent of traffic that is heavy, and cars are almost irrelevant to it.
3 sections · 1 calculator
Earned Value Indices
How three numbers become a forecast, why the schedule index lies at the end of a project, and what TCPI is really asking.
4 sections · 1 calculator
Numerical Goal Seek by Bisection
How the site inverts any calculator — and why bisection rather than Newton–Raphson is the correct choice here.
3 sections
Cut Lists and Bin Packing
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.
3 sections
Formwork Pressure
Why a column form sees full hydrostatic pressure and a wall form usually does not, and why temperature belongs in the equation.
3 sections · 2 calculators