1. Your measurements
You can type in feet and inches (13 ft 6 in, or 13' 6") or in meters, and use a comma or a point for decimals. Several areas can be added together, and openings such as doors and windows are subtracted where it matters.
2. Calculated in metric, shown in your units
Internally every calculator works in metric (meters, liters, kilograms) and converts only on the way in and out, using exact factors: 1 ft = 0.3048 m, 1 in = 25.4 mm, 1 US gallon = 3.785411784 L, 1 lb = 0.45359237 kg. That is why the same room gives the same result in either system.
3. Waste
Real jobs lose material to cuts, breakage, uneven surfaces and what stays in the bucket. Each calculator adds a default allowance based on the material and the layout, for example 10% for tile laid straight and 15% on a diagonal. You can change it, and every page has a table explaining the usual range.
4. Rounding to what you can buy
Quantities are never rounded in the middle of a calculation, only at the end, and packs are always rounded up: you cannot buy 22.4 boxes. Where a product comes in several sizes (paint cans, grout bags), we combine sizes to waste as little as possible, and switch to the larger size when the small ones would add up to most of it anyway.
5. Pack sizes by region
Material properties such as how far a gallon of paint goes are the same everywhere. Pack sizes are not: a bag of thinset is 50 lb in the US and 20 kg in the UK. Pack sizes follow the currency you choose in the header.
6. Cost
We never show made-up prices. If you enter your own price, you get three numbers: Low (no waste), Typical (with waste) and With waste, the cost of the full packs you will actually buy.
7. Where the figures come from
Coverage and consumption figures, such as square feet per gallon or kilograms of adhesive per square meter for each trowel size, come from manufacturer data sheets and industry guides. Each calculator page names the assumptions it uses, and you can change most of them under Advanced options to match the product you buy.
8. Testing
Every calculator has worked examples in imperial and metric. Before each release we check them automatically and test the pages in Chrome, Safari and Firefox.
Limits
Results are estimates. Actual use depends on the product, the surface, the installation method and site conditions. For structural work, electrics, gas and roofing, consult a licensed professional.
Formula changelog
- November 2026: first release of the Paint, Tile, Laminate Flooring, Wallpaper, Screed, Drywall, Plaster, Tile Adhesive, Grout and Paver calculators.