Unit Converter

How to use the unit converter

1. Choose what you are converting: length, weight, volume, area, temperature, speed, time, digital storage, pressure, energy or fuel economy.
2. Type the value.
3. Pick the From and To units.

The answer appears instantly with the conversion factor and the working. Below it, a table converts your value into every unit in that category, which is handy when you are not sure which unit you need.

The unit conversion formula

For most quantities, conversion is a single multiplication:

Value in new unit = value × (size of old unit ÷ size of new unit)

The converter stores every unit as a multiple of one SI base unit (the metre, kilogram, litre, square metre, second, byte, pascal or joule) and divides one by the other. To convert 100 cm to inches: 1 cm = 0.01 m and 1 in = 0.0254 m, so the factor is 0.01 ÷ 0.0254 = 0.3937008, and 100 × 0.3937008 = 39.37008 in.

Two kinds of units do not work this way. Temperature scales have different zero points, so they need an offset as well as a factor (see the temperature converter). Fuel economy units are reciprocals: mpg and km/L measure distance per fuel, while L/100 km measures fuel per distance, so the converter divides rather than multiplies.

Exact definitions used

Since the international yard and pound agreement of 1959, U.S. customary units have been defined exactly in metric terms. The converter uses these exact values from NIST:

Unit	Exact definition
1 inch	2.54 cm
1 foot	0.3048 m
1 mile	1,609.344 m
1 pound	0.45359237 kg
1 US gallon	231 cubic inches = 3.785411784 L
1 imperial (UK) gallon	4.54609 L
1 acre	43,560 sq ft = 4,046.8564224 m²
1 calorie (thermochemical)	4.184 J

Quick reference: the most searched conversions

Centimetres and inches

cm	inches		inches	cm
1	0.3937		1	2.54
5	1.9685		6	15.24
10	3.937		12	30.48
30	11.811		66 (5 ft 6 in)	167.64

Kilograms and pounds

kg	lb		lb	kg
1	2.2046		1	0.4536
5	11.023		10	4.5359
50	110.231		150	68.039
100	220.462		200	90.718

Other everyday conversions

From	To
1 foot	0.3048 metres
1 metre	3.28084 feet
1 km	0.621371 miles
1 mile	1.609344 km
100 mL	3.3814 US fl oz
1 litre	33.814 US fl oz
1 US cup	236.59 mL
1 acre	0.404686 hectares
1 m²	10.7639 sq ft
32 psi	2.206 bar
1 kWh	3,412.14 BTU
1 kcal	4.184 kJ

Cups, ounces and gallons: US vs UK vs metric

Volume is where most conversion mistakes happen, because the same name means different amounts in different countries. A US cup holds 236.59 mL, a metric cup used in Australia, Canada and many UK recipes holds 250 mL, and the “legal” cup on U.S. nutrition labels is 240 mL. A US fluid ounce is 29.5735 mL, while an imperial fluid ounce is 28.4131 mL. The difference grows with size: an imperial gallon is about 20% larger than a US gallon, which is also why UK mpg figures look higher than US ones for the same car. Choose the unit that matches where your recipe or label comes from.

Bytes: kB vs KiB

Storage makers and network speeds use SI prefixes, where kilo means 1,000. Operating systems often count memory in binary multiples of 1,024 but still call them KB, MB and GB. The IEC binary prefixes make the difference explicit: 1 KiB = 1,024 bytes, 1 MiB = 1,048,576 bytes and 1 GiB = 1,073,741,824 bytes. That is why a 500 GB drive shows about 465.66 GiB and a 1 TB drive about 931.32 GiB. Internet speeds are quoted in megabits per second, so a 100 Mbps connection moves at most 12.5 megabytes per second, since there are 8 bits in a byte.

Tips for accurate conversions

• Round only at the end. Rounding 1 inch to 2.5 cm adds a 1.6% error to every result.
• Check which ton, gallon or cup you mean. The US short ton is 2,000 lb, the UK long ton is 2,240 lb and the metric tonne is 1,000 kg (about 2,204.6 lb).
• For room sizes and flooring, the square footage calculator handles feet-and-inches measurements directly.
• For fuel budgets, the fuel cost calculator converts between mpg, km/L and L/100 km as part of the trip cost.