Unit Converter
Convert kg to lbs, cm to inches, Celsius to Fahrenheit and any length, weight, temperature, volume, area, speed or data unit, with the exact factor shown.
Every convention this page applies is named in the result rather than assumed. Your numbers stay in this browser.
Results
How to read this: the verdict describes how much room your numbers leave, not a decision or an offer. Change any input to see how much the result moves.
Assumptions and formula
Each unit carries a factor expressing it in the category’s base unit, taken from the defined values in NIST SP 811 and the 1959 international yard and pound agreement: the inch is exactly 25.4 mm, the pound exactly 0.45359237 kg, the US gallon exactly 231 cubic inches and the imperial gallon exactly 4.54609 litres. A conversion multiplies by the source factor and divides by the target factor. Temperature converts through kelvin, because Celsius and Fahrenheit differ in their zero as well as their degree.
Results are held at full precision and shown to the significant figures you choose. Digital storage offers both decimal units (kB, MB, GB) and binary ones (KiB, MiB, GiB), because a drive sold as 1 TB shows 931 GB in a system that counts in binary, and neither figure is wrong.
Worked example
A marathon of 26.2 miles is 26.2 × 1.609344 = 42.16 km. 20 °C is 20 × 9 ÷ 5 + 32 = 68 °F. Ten US gallons are 37.85 litres but 8.33 imperial gallons, because the imperial gallon is a fifth larger. One tebibyte is 1,024⁴ bytes, which is 1.0995 decimal terabytes.
Frequently asked questions
Why do a US gallon and a UK gallon give different answers?
Because they are different units with the same name. The US gallon is 231 cubic inches, 3.785 litres; the imperial gallon used in the UK is 4.546 litres, about 20% more. The pints differ too: 16 US fluid ounces against 20 imperial. A car doing 40 mpg in the UK is doing 33 mpg by US measure. This converter lists both explicitly and warns when you convert between them.
Why does my 1 TB drive show up as 931 GB?
Drive makers count in decimal: 1 TB is 1,000,000,000,000 bytes. Windows counts in binary but uses the decimal names: what it calls a GB is 1,073,741,824 bytes, properly a gibibyte (GiB). Dividing gives 931.3 GiB, and nothing is missing. The converter offers both sets of units so the two can be told apart.
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32: 20 °C is 20 × 1.8 + 32 = 68 °F. Going the other way, subtract 32 first, then multiply by 5/9. The 32 is there because the two scales put zero in different places, which is why temperature cannot be converted by a single multiplying factor like every other unit here. −40 is the one temperature that reads the same on both scales.
Are the conversion factors exact?
Yes for every unit here. Since 1959 the inch has been defined as exactly 25.4 mm and the pound as exactly 0.45359237 kg, and the yard, mile, ounce, ton, acre and US gallon follow from those by definition. The imperial gallon is defined as exactly 4.54609 litres. The result says when a factor is exact, and is rounded only for display.
What is the difference between a tonne, a ton and a long ton?
A tonne (metric ton) is 1,000 kg. A US ton, or short ton, is 2,000 lb, about 907 kg. A UK ton, or long ton, is 2,240 lb, about 1,016 kg. Shipping, mining and older British sources use the long ton; American freight uses the short ton; almost everything else uses the tonne. The converter labels all three so a figure cannot be silently misread.
What are the most common conversions people need?
Kilograms to pounds (multiply by 2.2046), centimetres to inches (divide by 2.54), km to miles (multiply by 0.6214) and Celsius to Fahrenheit (multiply by 1.8, add 32). A temperature converter is the odd one out because the scales do not share a zero, so the offset matters. A weight converter and a length converter are pure multiplication by a defined factor, and this measurement converter shows the factor it used beside the answer so any result can be checked by hand.
Is this a metric converter or does it work for imperial units too?
Both directions. As a metric converter it moves between metric units, millimetres to metres or grams to kilograms, and as a metric to imperial converter it crosses the systems, kilograms to pounds or litres to US gallons. A unit conversion calculator has to know which imperial you mean, because a UK gallon is 4.546 litres and a US gallon 3.785, and a UK pint is 568 ml against 473 ml in the US; this page lists both and warns when two units share a name but not a size.