About UnitPairs

UnitPairs is a small, single-purpose site: one page per unit pair, each with a live converter, a chart, the formula and a worked example you can check by hand.

Why pair pages instead of one mega-converter?

Most people arrive looking for one specific conversion — 170 cm in inches, 100 kg in pounds — and want the answer with the chart for neighbouring values, not a generic box they have to configure. Pair pages also let each conversion carry its own context: ruler fractions on the length pairs, the US-versus-imperial gallon warning on the volume pairs, the −40 crossover on the temperature pages.

The factors

All factors are the exact international definitions, as published by NIST: 1 inch = 2.54 cm, 1 foot = 0.3048 m, 1 mile = 1.609344 km, 1 pound = 0.45359237 kg, 1 ounce = 28.349523125 g, 1 US gallon = 3.785411784 litres, 1 square foot = 0.09290304 m². Where a unit is defined as a fraction of another (an ounce is a sixteenth of a pound), the page says so. Results are displayed to six decimal places and never pre-rounded.

Honest limits

Fractions of an inch are approximations to the nearest sixteenth, and every fraction readout states its own error. Temperature shortcuts and mental-math rules are labelled as shortcuts. UnitPairs is a reference tool — for engineering tolerances, medical dosing or legal metrology, verify against the governing standard for your application.