Math calculators

Everyday math tools that handle the arithmetic so you don’t have to. Percentages first — geometry, statistics, and equation solvers will join this cluster as we ship them.

The percentage calculator covers the four shapes the same question takes in real life: percent of a number, what percent is X of Y, percent change between two values, and the reverse-engineered original price given a final price and a discount. Each variant is a separate input rather than a single field that guesses your intent, because guessing wrong on percentage change versus percentage-point change is the source of more reporting errors than any other single arithmetic mistake. The area calculator covers eight 2D shapes, including Heron’s formula for triangles where you only have the three sides; the volume calculator covers eight 3D shapes the same way. The statistics calculator accepts a pasted dataset (one number per line, or comma-separated) and returns mean, median, mode, standard deviation, variance, percentiles, and the inter-quartile range together, since a single “average” is rarely the right summary on its own. All calculations run in double precision and never round prematurely.