Unit conversions, exact to the definition
Every converter on UnitPairs uses the exact international definition factors — 1 inch is 2.54 cm, 1 pound is 0.45359237 kg, 1 US gallon is 3.785411784 litres — never the rounded versions that drift. Pick a category and a pair below, or jump straight to a dedicated pair page with its own chart and worked example.
Every pair has its own page
A dedicated page per pair means the chart, the formula and the common values for that exact conversion are one click away — and length results also come as ruler fractions (170 cm = 66.9291 in, for example).
Length
- centimetres to inches — 1 cm = 0.393701 in
- inches to centimetres — 1 in = 2.54 cm
- metres to feet — 1 m = 3.28084 ft
- feet to metres — 1 ft = 0.3048 m
- kilometres to miles — 1 km = 0.621371 mi
- miles to kilometres — 1 mi = 1.609344 km
- centimetres to feet — 1 cm = 0.032808 ft
- inches to millimetres — 1 in = 25.4 mm
Mass & weight
- kilograms to pounds — 1 kg = 2.204623 lb
- pounds to kilograms — 1 lb = 0.453592 kg
- grams to ounces — 1 g = 0.035274 oz
- ounces to grams — 1 oz = 28.349523 g
- kilograms to stone — 1 kg = 0.157473 st
Temperature
- degrees Celsius to degrees Fahrenheit — 1 °C = 33.8 °F
- degrees Fahrenheit to degrees Celsius — 1 °F = -17.222222 °C
Volume
- litres to US gallons — 1 L = 0.264172 gal
- US gallons to litres — 1 gal = 3.785412 L
- millilitres to US fluid ounces — 1 ml = 0.033814 fl oz
Area
- square metres to square feet — 1 m² = 10.76391 ft²
- square feet to square metres — 1 ft² = 0.092903 m²
Two special tools
Height converter
Centimetres to feet and inches in the form people actually say out loud: 175 cm = 5 ft 8.9 in — and back.
Temperature chart
The full −40 to 100 °C range side by side with Fahrenheit, including the one point where the two scales agree.
Where the factors come from
The inch, foot, pound and gallon are not approximations of metric units — since the 1959 international yard and pound agreement they are defined in metric terms: a yard is exactly 0.9144 m, so an inch is exactly 25.4 mm and a foot exactly 0.3048 m; a pound is exactly 0.45359237 kg; a US gallon is exactly 231 cubic inches, which is 3.785411784 litres. UnitPairs stores those definition values and shows its working on every page, so a number you read here can be re-derived by hand. Displayed results are rounded to six decimal places; the underlying factors never are.
Why do other converters give slightly different answers?
Many use shortened factors such as 0.39 inches per centimetre or 2.2 pounds per kilogram. Those are fine for a rough idea but drift on larger values — at 100 kg the shortcut is already off by more than half a pound. This site uses the exact definitions throughout.
Is the gallon here the US or the imperial gallon?
The US gallon (3.785411784 litres). The imperial gallon, once used in the UK, is 4.54609 litres — about 20% larger — and is not used anywhere on this site. Volume pages say so explicitly.
Does anything I type leave my browser?
No. All conversion happens locally in this page; there is no server call and nothing is stored.