Methodology and reliability
How to interpret our calculations, check assumptions and report an error.
Formulas and worked examples
Calculator pages explain their units, formulas and assumptions alongside the tool. Worked examples make the arithmetic reproducible: moving from 80 to 100 is a 25% increase, and a 6/12 roof slope is about 26.5651 degrees. Examples illustrate the chosen assumptions; they are not supplier quotes or project specifications.
Checks and sources
We use automated calculation tests and worked examples to check formulas and conversions. Browser checks cover interactive flows such as changing units, rejecting invalid inputs and exporting results. Relevant source links appear on tool pages where provided. A source reference does not mean the source’s organization reviewed or approved this website.
Assumptions, rounding and external data
Check editable density, dimensions, price units, margins and rounding before using a result. Display precision can differ from calculation precision. Browser memory and format support affect file tools. Results obtained from external APIs depend on provider availability and freshness; a cached or estimated value is not a guarantee of current conditions.
Corrections and limits
A passing test does not prove every possible input is correct. If a result looks wrong, report the tool URL, units, inputs and expected output using non-sensitive example data. Calculators support planning and learning; they do not replace a project-specific professional assessment. Explanations and tools may be corrected as issues are identified.