Practical project math, without the guesswork

BuildingMath is a growing collection of single-purpose calculators for common home improvement and DIY projects — concrete, paint, mulch, gravel, tile, flooring, drywall, decking, fencing and more. Each calculator answers one material-estimation question and shows the full working, so you can see exactly how the number was reached rather than trusting a black box.

The site is built and maintained by JD Projects, a registered Danish sole proprietorship. It exists because estimating materials for a project is a question people ask over and over — "how many bags of concrete", "how much paint for this room" — and most answers online either hide their assumptions or bury the calculator under pages of filler. BuildingMath aims to do one thing well: give you a clear, honest estimate and explain it.

Accuracy is the point of this site, so we take it seriously. Every calculator ships with built-in test cases that must pass before the site is published — if a formula produces the wrong answer for a known example, the build fails. Formulas follow standard trade practice, including sensible waste allowances, and are checked against established industry references (for example, the concrete calculator is verified against published bag-yield data from manufacturers such as QUIKRETE).

That said, an estimate is a planning tool, not a final material order. Product yields vary by brand, site conditions differ, and local building codes and supplier ordering rules always take precedence. Before you buy or build, confirm the specifics with your materials supplier and, where relevant, a qualified professional. If you ever spot a result that looks wrong, please tell us — see the contact page — because getting the math right matters more to us than anything else on the site.