How our calculators work
Inputs and the calculation
Start with the measurements or specifications requested by the tool. Units matter: nominal dimensions, measured dimensions and product ratings are not automatically interchangeable. The tool should explain the formula, decision tree or reference data used to transform those inputs into an answer.
Read the result before shopping
The technical result should stand on its own. A recommended range or equipment class can follow it, with an explanation of assumptions and rounding. Merchant links, when present, are optional examples; opening a shop must not be necessary to see or understand the result.
Unsupported situations
A tool can reject an input or return no reliable match when its model does not cover the situation. This is preferable to inventing a recommendation. An estimate cannot account for conditions that were never included in the model.
Check the methodology
Use the methodology and sources on the individual tool to understand its scope. For work involving hazards or rated equipment, check the relevant manufacturer instructions and applicable requirements. If the explanation and result disagree, report the tool URL, inputs and observed output through our contact page.
Policy published: 10 September 2026