Unit Converter

Converting a value

1. Choose a category: length, weight, volume, area, speed, data or temperature. The two unit menus refill with the units for that category.
2. Type a number in the left box. Decimals and negative numbers are accepted, and the right box shows the answer as you type.
3. Pick the starting unit in the left menu and the target unit in the right one. Press Swap to reverse the direction without retyping.

Length opens on miles to kilometres, since that is a very common request. Other categories start with their first two units. The output box is read-only, so select its text to copy it.

How the maths works

For every category except temperature, each unit is stored as a factor relative to one base unit: metres for length, kilograms for weight, litres for volume, square metres for area, metres per second for speed and bytes for data. The converter multiplies your value by the starting unit's factor to reach the base, then divides by the target unit's factor. So 5 miles becomes 5 × 1609.344 = 8046.72 metres, and dividing by 1000 gives 8.04672 km.

Temperature cannot use a single multiplier because Celsius, Fahrenheit and Kelvin have different zero points. The page converts to Celsius first (Fahrenheit minus 32, times 5/9; Kelvin minus 273.15) and then to the target (Celsius times 9/5 plus 32; or plus 273.15). For example 100 °F becomes 37.777778 °C and 0 °C becomes 273.15 K.

Results are rounded to 8 significant digits, with trailing zeros dropped. Very large or very small answers may appear in exponent form, such as 1e-7.

Worked examples

• Body weight: 70 kg is about 154.32 lb. Going the other way, 12 stone is about 76.2 kg, because the stone is stored as 6.35029318 kg.
• Cooking: 1 US gallon is 3.7854118 L, and 1 US cup is about 236.59 mL. A UK gallon is larger at 4.54609 L, which is roughly 1.2 US gallons, so a recipe or fuel figure from Britain can differ noticeably from an American one.
• Speed: 100 km/h is about 62.137 mph, and a knot is 0.514444444 metres per second.
• Land: one hectare is 10,000 square metres, and an acre is 4046.8564224 square metres, so a hectare is about 2.47 acres.
• Storage: a 500 GB drive holds about 465.66 GiB, which is why a new drive looks smaller in an operating system that reports in binary units.

Decimal versus binary data units

The data category lists both families. KB, MB, GB and TB use powers of 1000, matching how drive makers and network speeds are quoted. KiB, MiB, GiB and TiB use powers of 1024, matching how memory is addressed and how some operating systems show file sizes. 1 GB is 1,000,000,000 bytes while 1 GiB is 1,073,741,824 bytes, a gap of about 7 percent that widens at the terabyte scale: 1 TB is only about 0.909 TiB. If two tools disagree about a file size, check which family each one uses.

Common uses

• Travel and shopping: road distances, luggage limits, clothing and product specifications between metric and imperial.
• Cooking and baking: converting US cups and fluid ounces against litres and millilitres.
• Home projects: floor space in square feet against square metres, and lengths in inches against millimetres.
• Study and technical work: checking homework, datasheets or bandwidth figures.

Tips and limits

• Volume and weight are different things. This tool does not turn cups into grams because that depends on the ingredient's density.
• Fluid ounces and cups here are US measures. UK and metric cups are not in the list, and the only UK volume unit is the imperial gallon.
• The weight units are units of mass, so pounds and ounces mean the avoirdupois measures used in everyday trade. Troy ounces for precious metals are not included.
• Temperature input is not range-checked, so a value below absolute zero will produce a number even though it is physically impossible.
• Currency, time and fuel economy conversions are not included, since they need rates or inverse relationships rather than a fixed factor.

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