Every result here is arithmetic on the numbers you type. This page says what the arithmetic is and where you must supply a number yourself.
What is calculated
- Volumes: length times width times depth, with inches turned into feet, then cubic feet divided by 27 to get cubic yards.
- Areas: length times width for a floor, and the room's perimeter times the wall height for paint.
- Extra: the percentage you choose is added on top, and counts of bags, boxes or gallons round up.
What you must read yourself
The yield of a bag of concrete, the size of a bag of mulch, the coverage of a can of paint, the coverage of a box of flooring and the weight of a yard of gravel all depend on the product. The calculators start with an example value in those fields and ask you to replace it with the number on your label or from your supplier.
What the results do not cover
- Shapes other than rectangles: split a shape into rectangles and add the results.
- Rebar, forms, base layers, sealer, primer or underlayment.
- Building rules, permits or the strength a project needs.
The same inputs always give the same outputs, and the page tests check that the numbers in the examples equal the calculator's. Last checked 2026-10-16.