Methodology

Why these estimates behave predictably

Every tool declares the formula, the inputs it uses, the assumptions it makes and the limits of its model. Results use the measurements and reference values shown in the form. Named supplier or product examples are editable and identified beside the relevant field. A reference is not a guarantee for a different product.

Units and exact conversions

All arithmetic is metric internally and uses exact rational quantities with international (NIST) unit definitions. Feet, inches and fractions such as 7 1/2 are accepted at entry. Unit selection changes presentation, never the underlying value: 1 in equals 25.4 mm exactly, 1 yd equals 0.9144 m and 1 US gallon equals 3.785411784 L.

Rounding and purchasing

Decimals are carried through the calculation and rounding happens at the end. Material allowances and waste factors are applied once, under the formula shown on the page. Bags, boards, rolls and other whole purchasing units round up only at the purchasing step, so you are never told to buy 12.3 bags. Where geometry involves π or a square root, documented bounds are used; a knife-edge purchase boundary asks you to confirm the measurement instead of silently rounding.

Money and currency

Prices are your own inputs; the site does not supply price lists or convert exchange rates. USD, EUR and GBP round half-up to two decimals, and JPY rounds to whole yen. Selecting a currency changes the display symbol only, not the numeric result.

What we test

Automated checks cover worked examples, exact unit conversions, rounding boundaries, invalid inputs and targeted regressions. Separate checks cover draft editing, numerical verification, publication controls and private reports. Browser samples inspect the displayed results and controls. The scope and results are recorded for each release; passing tests does not establish professional certification or suitability for every project.

Review status

Automated verification and review are recorded separately against the current calculator definition and software version. AI agents assist with editorial and arithmetic review; implementation follow-ups are attributed separately, and AI review records identify their actual role and limitations. These are not licensed human professional sign-offs. Electrical and pool-chemistry pages are published only within their stated educational arithmetic scope after source and model review. They do not certify an installation, choose a treatment target or establish safety. Actual installation and treatment decisions require qualified advice and the exact product instructions. We do not invent reviewer names or credentials.

Corrections

Each release is versioned, and corrected behaviour is listed on the corrections page. If a result looks wrong, send the inputs, units, result and expected value through the report form and the site owner will try to reproduce it.