Last updated: October 23, 2026. This page explains how TrowelMath creates, checks and updates its calculators and guides.
Our standards
- Primary sources first. Data comes from official statistics, standards bodies or the original publisher, and each page names its source and the period covered.
- Show the working. Each calculator states its formula and assumptions, with a worked example you can verify.
- Test before publishing. Our automated tests cover unit conversions between feet, inches, yards and metres, bag rounding and waste allowances. A failing test blocks publication.
- Independence. Advertisers and affiliate partners have no say in what we publish or how a result is calculated.
Methodology
Volumes are length × width × depth with the waste allowance you choose. Bag counts use manufacturer yields (40/50/60/80 lb = 0.30/0.375/0.45/0.60 cu ft). Paint uses 350 sq ft per gallon unless you change it; door and window deductions are 20 and 15 sq ft. Room AC sizes follow the ENERGY STAR chart and adjustments.
Sources we use
- Manufacturer bag-yield data for standard concrete mix (40/50/60/80 lb bags)
- ENERGY STAR room air conditioner sizing chart
- Typical paint coverage of 350 sq ft per gallon (adjustable on every page)
How content is written
Pages are researched and edited by Alex. We use software, including AI writing tools, to help draft explanations and to generate pages from structured data (for example, one page per country or per loan amount). Every figure comes from the calculator engine or a cited data set, not from a language model, and generated text is reviewed against the source before publication. Pages that would add little beyond an existing page are excluded from search indexing.
Updates and corrections
We refresh data when the publisher releases a new edition and record the date on each page. If you spot an error, please contact us; confirmed errors are corrected promptly and the page date is updated.
Limits
Calculators give estimates for general information. They are not personalised advice; see our terms of use.