How BuilderMath calculates

Sizes as a tape reads them

Every length can be typed in feet, inches and a fraction of an inch down to 1/16. A size such as 3-1/2 typed into the inches box is not guessed at: the field names the problem and offers the fix, 3 in and 1/2 in the next box. Nothing is worked out until every size reads right, so a half-typed form never shows a total.

Shapes, added and taken away

A job is one shape or several. An L-shaped room is two rectangles added together; a hearth, an island or a pool is a shape taken away. Each piece is worked out on its own with its geometry formula, then the pieces are added and the cut-outs subtracted. The drawing shows every piece to one scale, with the sizes you typed on it.

Units

Conversions use the definitions of the units, not rounded factors: a foot is exactly 0.3048 m, a square yard is 9 square feet, a cubic yard is 27 cubic feet and a US gallon is 231 cubic inches. The calculators keep full precision until the last step and round only what they print.

Rounding and the extra

What you buy is rounded up, never down: whole square feet of flooring, whole bags, ready-mix in the steps a supplier sells. The extra for waste, spillage or settling is its own line, with the amount a named source advises, and you can change it. The total before the extra is always printed next to it.

Sources and checks

Every figure that is not geometry or a unit definition, such as a bag yield, a coverage or a thickness, names the document it comes from. The documents are listed by name under each calculator with the date they were last checked; the site does not link out. Each calculator is tested against worked examples done by hand before it is published.

Questions or a number that looks wrong: contact@buildermath.org. More about the site: About BuilderMath.