Material estimates are only useful if you can trust them. This page explains where our figures come from, how the calculators work, and what we do when something changes.
Where the numbers come from
We use, in this order of preference:
- Manufacturers’ published data: bag yields on concrete and mortar data sheets, coverage rates printed by paint, primer, stain, grout and thinset makers, carton sizes for flooring, installation guides for decking and pavers.
- Government and building-science sources: for example ENERGY STAR and the US Department of Energy for insulation R-values.
- University extension services: for lawn seeding rates, topsoil and mulch depths.
- Reputable trade and supplier references when no manufacturer or public source covers a point. When we rely on one of these, the article names it.
Every article lists its sources at the end with links, and the date the figures were last checked.
How the calculators work
Each calculator uses straightforward geometry (area, volume, unit conversions) plus the product figure it depends on, such as how many cubic feet an 80 lb bag of concrete yields. The formula is printed under every result and explained with a worked example in the article, so you can repeat the math by hand.
Where a figure varies by brand (paint coverage, grout coverage, insulation bags), the calculator lets you type in the number from your product label. The label on the product you buy always wins over a general figure.
The calculators run entirely in your browser. Nothing you type is sent to us or stored.
How articles are written
Articles are drafted with the help of AI writing tools, working from the sources above, under the direction of Jorge Trigo, who is responsible for everything published here. Before anything goes live:
- every product figure is checked against the linked source;
- every number in a table or worked example is produced by the same calculator code you use on the page, not typed by hand;
- every calculator is tested with known inputs.
We don’t publish invented statistics, testimonials or “we tested” claims. When something can’t be confirmed from a reliable source, the article tells you to check the label or ask your supplier instead of guessing.
What we don’t cover
We stay away from structural design (beam, footing and retaining-wall engineering), electrical and gas work, and hazardous-material removal. Where a project needs a permit, an inspection or an engineer, we say so.
Corrections and updates
Manufacturers change formulas and bag sizes, and codes get updated. If you find an error, please email us through the contact page with the page address and what you think is wrong. We review every correction and update the page and its “last checked” date when a change is confirmed.