Unit Converter

About Unit Converter

Ten categories: length, weight, temperature, volume, area, speed, time, data, pressure and energy. Type a value into any unit and every other unit in the category updates at once. Each category has one base unit (meter, kilogram, kelvin, liter and so on), and every unit is defined as a fixed factor of that base. Temperature is the exception because the scales have different zero points, so it uses a linear formula instead of a factor, and values below absolute zero are rejected.

Customary units like the inch and the pound are now defined exactly in metric terms, so those conversions carry no error. The ones to watch are units that mean different things in different countries, like the gallon, and units that are legally obsolete but still in everyday use.

The inch and the pound have been metric since 1959

In 1959 the United States, the United Kingdom, Canada, Australia, New Zealand and South Africa agreed on the international yard of exactly 0.9144 m and the international pound of exactly 0.45359237 kg. The inch (25.4 mm) and the foot (0.3048 m) follow exactly. Before that, the American and British inches differed by a few parts per million.

That is why 5 ft in this tool is exactly 1.524 m and 100 lb is exactly 45.359237 kg. The mile is exactly 1,609.344 m, and the ounce, one sixteenth of a pound, is 28.349523125 g.

US gallons versus imperial gallons

Every volume unit here other than the metric ones is US customary: gallon, cup, fluid ounce, tablespoon, teaspoon. The US gallon is defined as 231 cubic inches, which is 3.785411784 L. The imperial gallon used in the UK is 4.54609 L, about 20% larger. So a British car rated at 50 mpg is not the same as an American one rated at 50 mpg; the British figure corresponds to roughly 42 US mpg. The tool lists the imperial gallon separately as Gallon (UK); one imperial gallon is 1.200949926 US gallons.

Within US units the relationships are exact: 1 gallon = 16 cups = 128 fl oz = 256 tablespoons = 768 teaspoons, and the tool returns exactly those numbers. Note that the US cup (about 237 mL) differs from the 250 mL metric cup used in Australia and elsewhere, and the US fluid ounce (29.57 mL) differs from the imperial one (28.41 mL).

Korean and Japanese traditional units

The area category includes the Korean pyeong, defined as a square six cheok on a side (one cheok = 10/33 m), which gives exactly 400/121 m², about 3.3058 m². Korea's Measures Act bars units outside the legal SI-based set from trade and advertising, and since July 2007 the government has enforced that against pyeong in real estate and don in gold sales. Listings now say 84 m², though people still call it a '34-pyeong' apartment. That everyday figure usually refers to supply area, which includes shared space; the private 84 m² itself is 25.41 pyeong.

Japan's tsubo is the same square of six shaku and the same 400/121 m². Japanese listings also give room sizes in jo (tatami mats); under the real-estate advertising fair-competition rules, one jo must mean at least 1.62 m². Neither jo nor the Korean weight units (a geun of meat is conventionally 600 g, a don of gold 3.75 g) are built into this tool.

Why a 1 TB drive shows 931 GB

Drive manufacturers use SI prefixes, so their 1 TB is 10^12 bytes. Windows counts in steps of 1,024 but still labels the result KB, MB and GB. The IEC introduced KiB, MiB and GiB for the 1,024-based units to end this confusion, and the tool keeps the two apart: KB, MB, GB and TB step by 1,000, while KiB, MiB, GiB, TiB and PiB step by 1,024. Enter 1 TB and you get 931.3225746 GiB, which Windows displays as 931 GB on a new 1 TB drive.

Worked examples

How to use it

1. Choose a category.
2. Type a value into the unit you know; thousands separators are fine. Use a point for decimals; a comma that cannot be a thousands group, as in 1,5, is read as a decimal comma.
3. Every unit in the category updates immediately. Copy what you need.

Frequently asked questions