How we calculate
Every calculator on this site uses basic geometry and standard coverage figures. Here are the formulas and defaults, so you can check them or change them for your own materials.
| Calculator | Assumptions (all editable on the page) |
|---|---|
| Paint | Walls = perimeter × height, minus 20 sq ft per door and 15 sq ft per window; coverage 350 sq ft per gallon |
| Concrete | 27 cubic feet per cubic yard; an 80-lb bag makes about 0.6 cu ft and a 60-lb bag about 0.45 cu ft; 10% waste |
| Mulch | Volume ÷ 27 for cubic yards; bags of 2 or 3 cubic feet |
| Gravel | Volume plus 10% settling; 1.4 tons per cubic yard unless you change it |
| Flooring and tile | Area plus a 10% waste allowance, rounded up to whole boxes or tiles |
| Fence | Posts = sections + 1; rails, picket width and gaps are editable |
| Deck | Boards = area plus waste ÷ one board's coverage; joists = length ÷ spacing + 1 |
| Grass seed | Area ÷ 1,000 × the seeding rate on your seed bag |
| Repair vs replace | Three common rules of thumb; the verdict follows the majority |
Accuracy and corrections
Product sizes, coverage rates and weights differ between brands, so the label on your product always wins over our defaults. Prices are never built in. You enter your own so the cost matches your store. Last reviewed October 26, 2026. If you find an error, please tell us and we will fix it.