Seven quantities, one base unit each
Each category converts through a single base unit: metres for length, kilograms for mass, litres for volume, square metres for area, metres per second for speed and bytes for data. Your value is multiplied by the factor of the "from" unit and divided by the factor of the "to" unit. Temperature is the exception, because its scales have different zero points as well as different step sizes, so it goes through Celsius with proper offsets.
The units available:
- Length: mm, cm, m, km, in, ft, yd, mi, nmi (nautical mile).
- Mass: mg, g, kg, t (metric tonne), oz, lb, st (stone).
- Volume: ml, l, m3, tsp, tbsp, cup, pt, qt, gal, floz.
- Area: mm2, cm2, m2, ha, km2, in2, ft2, ac (acre), mi2.
- Speed: m/s, km/h, mph, kn (knot), ft/s.
- Data: B, KB, MB, GB, TB, KiB, MiB, GiB, TiB.
- Temperature: C, F, K.
Where the factors come from
Most imperial units are defined exactly in metric terms by the 1959 international yard and pound agreement. An inch is exactly 25.4 mm, a foot 0.3048 m, a mile 1,609.344 m and a pound exactly 0.45359237 kg. A nautical mile is exactly 1,852 m, an acre 4,046.8564224 m². These are definitions, not measurements, so 1 mi = 1.609344 km is exact.
Results show up to 10 significant digits with trailing zeros removed. Very large or very small results switch to scientific notation: 1 TB in bytes shows as 1e+12, and 1 mg in tonnes as 1e-09. The swap button exchanges the two units and keeps your number, so 5 mi → km becomes 5 km → mi.
US cups, pints and gallons
All the kitchen and liquid units in the volume list are US customary measures:
- 1 US cup = 236.588 ml
- 1 US pint = 473.176 ml, 1 quart = 946.353 ml
- 1 US gallon = 3.785 l
- 1 US fluid ounce = 29.574 ml, 1 tablespoon = 14.787 ml, 1 teaspoon = 4.929 ml
This matters for British, Canadian and older Australian recipes and for fuel figures. The imperial pint is 568 ml and the imperial gallon 4.546 l, about 20% larger, and those are not in the list. To convert an imperial gallon, enter 4.54609 l. A UK recipe asking for "1 pint of milk" means 568 ml, not the 473 ml shown for pt.
Cooking cups have their own variations: Australia, New Zealand and Canada often use a 250 ml metric cup. For dry ingredients, cups measure volume, not weight, and a cup of flour weighs about 120–130 g while a cup of sugar is about 200 g. Converting cups to grams requires the ingredient's density, which no unit converter can know.
The t in the mass list is the metric tonne of 1,000 kg. The US short ton is 907.2 kg and the British long ton 1,016 kg.
Bytes, KB and KiB
Data size is where most confusion comes from. The International Electrotechnical Commission defined two sets of prefixes in 1998:
- Decimal: 1 KB = 1,000 bytes, 1 MB = 1,000,000, 1 GB = 10^9.
- Binary: 1 KiB = 1,024 bytes, 1 MiB = 1,048,576, 1 GiB = 1,073,741,824.
Drive makers, network equipment and macOS use decimal units. Windows and many Linux tools calculate in binary units but often label them KB, MB and GB. That is why a "1 TB" drive appears as about 931 GB in Windows: 10^12 bytes divided by 1,024³ is 931.3 GiB. RAM is a binary quantity, so 16 GB of memory really is 16 GiB.
Network speeds are quoted in bits, not bytes, and bits are not in this list. Divide megabits per second by 8 to get megabytes per second: a 100 Mbit/s connection moves at most 12.5 MB/s.
Temperature and speed specifics
Temperature conversions use the exact formulas. Fahrenheit to Celsius subtracts 32 and multiplies by 5/9, so 100 °F is 37.78 °C, and −40 is the same on both scales. Kelvin is Celsius plus 273.15 with no degree sign; 0 K, absolute zero, is −273.15 °C. Negative inputs work for every unit, though a negative length or mass makes no physical sense.
For speed, 1 m/s = 3.6 km/h, so 60 mph is 96.56 km/h. Knots are used at sea and in aviation; 1 knot is one nautical mile per hour, exactly 1.852 km/h.
For other conversions on the site, the timestamp converter handles dates and Unix time, and the color converter translates between HEX, RGB and HSL. All arithmetic here runs in your browser and works offline once the page has loaded.