MathBench

Home & Hobby Calculators

Hobby math fails quietly: a circle skirt cut with the wrong radius wastes three yards of fabric, curtains ordered without the pattern repeat come up a panel short, and a pool dosed by guesswork swings between cloudy and eye-stinging all summer. These calculators do the arithmetic the project actually depends on — waist-to-radius geometry, fullness ratios and repeat rounding, chemical doses per ten thousand gallons — and show the formula each time so you can adapt it when your project is the exception.

The sewing tools speak the units of the fabric store: yards off the bolt at real fabric widths, strips per width-of-fabric, allowances stated instead of assumed. The pool tools follow public-health guidance from the CDC's Model Aquatic Health Code for target ranges, and always show the dose math per gallon of your actual water volume. Measure twice, calculate once, and check the worked example on each page against your own numbers before you cut fabric or open a chemical bucket.