Pick what you are converting – length, weight, volume, area, speed or temperature – then the two units. The most common pair is filled in for you (inches to centimeters, pounds to kilograms, US gallons to liters, acres to hectares, mph to km/h, °F to °C), and the result appears with the same amount in other units of its kind.
What the converter covers
| Kind | Units |
|---|---|
| Length | mm, cm, m, km, inch, foot, yard, mile, nautical mile, shaku, chi |
| Weight | mg, g, kg, metric ton, ounce, pound, stone, US and UK tons, troy ounce, carat, tola, jin, liang, kan |
| Volume | mL, L, m³, US and UK teaspoons to gallons, metric and Japanese cups, the US “legal” cup, oil barrel |
| Area | cm², m², are, hectare, km², in², ft², yd², acre, mi², tsubo / pyeong, mu, rai |
| Speed | km/h, m/s, mph, knot, ft/s |
| Temperature | °C, °F, kelvin |
Every unit has its own entry, even when two share a name, so a UK pint is never mistaken for a US pint (568 mL against 473 mL).
Traditional units still in daily use
Metric is official almost everywhere, but older units live on in markets, land registers and kitchens. These are the ones people most often need to convert, with their legal definitions:
| Unit | Where | Metric | US equivalent |
|---|---|---|---|
| Tsubo / pyeong | Japan, South Korea, Taiwan (floor area) | 3.3058 m² | 35.58 ft² |
| Mu | China (farmland) | 666.67 m² | 0.1647 acres |
| Rai | Thailand (land) | 1,600 m² | 0.3954 acres |
| Jin | China (food markets) | 500 g | 1.1023 lb |
| Liang | China | 50 g | 1.7637 oz |
| Tola | South Asia, the Gulf (gold) | 11.6638 g | 0.375 troy oz |
| Shaku | Japan (carpentry) | 30.30 cm | 11.93 in |
| Kan | Japan (pearls) | 3.75 kg | 8.267 lb |
A 25-tsubo apartment in Tokyo is 82.6 m² (890 ft²); a 10-rai plot in Thailand is 1.6 hectares (3.95 acres).
Area: acres, hectares and square feet
| 1 acre | 0.4047 ha |
| 1 hectare | 2.4711 acres |
| 1 square mile | 2.59 km² (640 acres) |
| 1 m² | 10.764 ft² |
To convert a floor area from square meters to square feet, multiply by 10.764: a 70 m² apartment is 753 ft².
How the conversions work
All units of one kind are stored as an exact multiple of one base unit – the meter, kilogram, liter, square meter or meter per second. Converting means multiplying by one factor and dividing by the other, so there is no rounding until the result is shown. Temperature is the exception: Fahrenheit and Celsius have different zero points, so the converter goes through kelvin.
The factors come from the US National Institute of Standards and Technology (NIST), the International Bureau of Weights and Measures (BIPM) and the UK Weights and Measures Act; the traditional units follow the laws that define them in Japan, China, Thailand and India.
Once zet4u is saved on your device, every unit here works offline – on a plane, abroad or anywhere without data.
Frequently asked questions
Are these conversion factors exact?
Yes, where the definition is exact. The inch (2.54 cm), pound (0.45359237 kg), US gallon (3.785411784 L) and UK gallon (4.54609 L) are defined exactly, so the results are exact up to the decimals shown.
Why are there two gallons, two tons and several cups?
Countries kept different traditional units under the same name. The converter keeps them apart: a US gallon is 3.785 L and a UK gallon 4.546 L; a short ton is 907 kg and a long ton 1,016 kg.
How big is a tsubo or a pyeong?
Both are 400/121 square meters, about 3.306 m² or 35.6 ft². They are still used for apartments and land in Japan, South Korea and Taiwan.
How many square meters is a mu or a rai?
A Chinese mu is 666.67 m² (one fifteenth of a hectare); a Thai rai is 1,600 m². Farmland in China and Thailand is still bought and sold in these units.
Sources
- NIST Special Publication 811: Guide for the Use of the SI, Appendix B (conversion factors)
- BIPM: The International System of Units (SI Brochure), 9th edition
- UK Weights and Measures Act 1985, Schedule 1
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