How we calculate
Every calculator answers one question — how much should I buy? — using plain geometry and published product figures. Here are the rules behind the numbers.
Measure, convert, calculate
Whatever units you type — feet, inches, fractions like 3 1/2, feet-and-inches like 10' 6", meters or centimeters — they're converted to exact SI values first (1 in = 2.54 cm exactly). The formula runs on those, and the answer is converted back to the units you shop in.
Extra for waste, built in
Real jobs lose material to cuts, spills, settling and compaction. Each calculator adds a typical allowance — for example 10% for concrete and tile, 5% for mulch. It's always shown next to the answer and you can change it under Options.
Rounded the way stores sell
- Bags, boxes, sheets and rolls are always rounded up to whole units — 41.2 bags means buy 42.
- Bulk orders round up to the next ¼ cubic yard or ¼ m³.
- Paint is packed into the cans that cover the job at the lowest typical price, e.g. 2 gallons + 1 quart.
- Volumes and weights show about three significant figures — more digits would suggest precision that measuring tapes and bag labels don't have.
Assumptions you can check
Each calculator lists its assumptions — bag yields, material densities, paint coverage — right below the formula, and Show the math reveals every intermediate value. Material properties vary by brand and supplier, so treat the answer as a well-founded estimate and check product labels, especially for structural work.
Privacy
There's no sign-up. Calculations run entirely in your browser; your measurements are kept only in the page address (so you can bookmark or share a result) and your unit preference in your browser's local storage.