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cm ↔ inches, m ↔ feet
Everyday length conversions for DIY, sewing, travel and screens.
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kg ↔ lbs, g ↔ oz
Weights for cooking, shipping, fitness and groceries.
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°C ↔ °F ↔ K
Temperature for weather, recipes and science.
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Unit converter
Convert length, weight, temperature, volume, area, speed, time and data — instantly, with metric and imperial units side by side.
This value in every unit
🔒 Conversions run entirely in your browser. Tap any unit below to copy it.
Why conversions are done through a base unit
Converting between every pair of units directly would need a table growing with the square of the number of units, and each entry would be an opportunity for a slightly different rounding. Instead this converter takes the approach every measurement system uses: convert the input to one canonical base unit for its dimension — metres, kilograms, seconds — then convert from that base to the target.
The benefit is that each unit needs exactly one factor and the conversions stay mutually consistent. The cost is one extra floating-point operation, and it is worth understanding what that does. Binary floating point cannot represent most decimal fractions exactly, which is why 0.1 + 0.2 famously yields 0.30000000000000004 in JavaScript and almost every other language. Each conversion step introduces a rounding of roughly one part in ten quadrillion, so a two-step conversion can return 2.9999999999999996 where you expected 3.
Results are therefore rounded for display rather than shown raw. For engineering work, keep the full-precision value through your calculation and round once at the end — rounding intermediate results and then multiplying is how small errors become visible ones.
Units that are not what their name suggests
The gallon is the classic trap: the US liquid gallon is 3.785 litres, the imperial gallon used in the UK is 4.546 litres, and they differ by about 20 percent. Pints, quarts and fluid ounces inherit the discrepancy, and the US fluid ounce and imperial fluid ounce differ as well, though only by four percent — enough to matter in a recipe, small enough to go unnoticed.
Tons are worse, because there are three. The US short ton is 2,000 pounds, the imperial long ton is 2,240 pounds, and the metric tonne is 1,000 kilograms, roughly 2,205 pounds. A quoted "ton" without a qualifier is ambiguous by up to twelve percent.
Mass and weight are also routinely conflated. The kilogram measures mass; the newton measures force. A pound is used for both, as pound-mass and pound-force, and the two are numerically equal only in standard Earth gravity. Any conversion between a kilogram and a newton is silently assuming 9.80665 m/s².
Temperature does not scale like anything else
Every other conversion here is a pure multiplication, because the scales share a zero: zero metres is zero feet, so doubling the input doubles the output. Temperature scales do not share a zero, which makes the conversion affine rather than linear — multiply, then add an offset.
This has a consequence that catches people out constantly: you cannot convert a temperature difference with the temperature formula. A rise of 10 °C is a rise of 18 °F, not 50 °F, because the offset applies to a point on the scale and not to an interval. If you are converting a tolerance, a gradient or a change over time, apply only the ratio — nine fifths between Celsius and Fahrenheit, one to one between Celsius and Kelvin.
Kelvin is the exception that proves the rule: it shares absolute zero with Rankine and has the same degree size as Celsius, so Celsius to Kelvin is a pure offset of 273.15 with no scaling at all.
Unit converter FAQ
What can I convert?
Length, weight, temperature, volume, area, speed, time and digital storage, each with metric and imperial units.
Is it accurate?
Yes — conversions use precise factors and update live, plus a table showing your value in every unit of the category.
Is it free and private?
Completely free, no sign-up, and everything runs locally in your browser.
Why do I sometimes get a result like 2.9999999999999996?
Binary floating point cannot represent most decimal fractions exactly, so each conversion step rounds very slightly. Displayed results are rounded to a sensible precision; keep full precision through a multi-step calculation and round only at the end.
Which gallon does this use?
Both are offered separately, because the US liquid gallon (3.785 L) and the imperial gallon (4.546 L) differ by about 20 percent. The same applies to pints, quarts and fluid ounces.