61 categories · 754 units · exact arithmetic
The unit converter that doesn't round early
Most converters turn every factor into a floating-point number before you have typed anything, and quietly lose digits. This one keeps conversion factors as exact fractions and rounds once, at the end — so you can ask for fifty significant figures and get fifty correct ones.
Most-used conversions
- cm → in
- kg → lb
- °C → °F
- m → ft
- L → gal
- km/h → mph
- km → mi
- g → oz
- psi → bar
- kWh → J
- GB → GiB
- hp → kW
- mpg (US) → L/100 km
- ac → m²
- ° → rad
- N·m → lbf·ft
Every converter
Common converters
Engineering
Heat & thermodynamics
Fluids
Electricity
Magnetism
Light & optics
Radiology
Why exact arithmetic matters
Nearly every unit in daily use is defined as an exact fraction of an SI unit. An inch is exactly 25.4 millimeters. A pound is exactly 0.453 592 37 kilograms. A pound per square inch is exactly 6894.757 293 168 361 336 7… pascals — a repeating decimal, because the definition works out to a fraction with 127² in the denominator.
A converter built on 64-bit floats has about 15–17 usable digits and accumulates a small error at every step. For a recipe that never matters. For a tolerance stack, a calibration record, or a physics problem set, it eventually does. This site stores every factor as a ratio of arbitrary-precision integers and does the whole conversion in exact rational arithmetic, so the only rounding happens when the number is printed.
Where a unit genuinely is irrational — anything involving π, or a logarithmic unit like the decibel — the site says so, and falls back to a 50-digit computation instead of pretending. How the maths works →