Calculation methodology
This page documents the standards every calculator formula on this site is held to before and after launch.
QA layers
- Formula review — the mathematical model and assumptions are checked against a reference source.
- Known-answer tests — a minimum of three test cases per calculator, including at least one edge case.
- Unit conversion tests — metric and imperial conversions are verified independently of the core formula.
- Input validation tests — zero, negative, decimal, empty, unusually large and invalid combinations are checked.
- Post-launch spot checks — re-run after deployment and whenever formula code changes.
Rounding policy
Calculation precision is kept internally throughout — rounding is applied only to displayed outputs. Where a rounding convention could materially affect a purchasing or construction estimate, we document it on the relevant calculator page and show any waste or safety allowance as a separate, visible line rather than folding it into the base calculation.
Assumption policy
For material densities, construction conventions, tax rules, overtime rules or any variable that differs by location or source, the calculator makes its assumption visible on the page and allows you to override it where practical. No calculator on this site implies legal, tax, engineering or professional advice — each is a general estimator.
Found a calculation you believe is incorrect? Please let us know — formula errors are treated as launch-blocking issues.