How to use the unit converter
- Choose what you are converting. Pick Length, Weight, Volume or Temperature. The unit lists change to match.
- Type the value. Decimals are fine, and you can paste numbers with thousands separators such as 1,250.
- Pick the From and To units. The answer appears straight away. Press Swap to convert the other way, for example from centimetres back to inches.
- Read the extras. Every result also shows the multiplication used and the same amount in every other unit of that type. Lengths are also shown in feet and inches and as a tape-measure fraction to the nearest 1/16 inch, and weights are shown in pounds and ounces.
The converter starts with a common seller question: how many centimetres is a 13 inch bag? The answer is exactly 33.02 cm, because one inch is defined as exactly 2.54 cm.
The exact conversion factors we use
Since 1959 the inch, foot, yard and pound have been defined in terms of metric units, so most conversions are exact rather than approximate. The calculator uses these definitions, as listed by the US National Institute of Standards and Technology (NIST):
- Length: 1 inch = 2.54 cm exactly; 1 foot = 12 inches = 30.48 cm; 1 yard = 3 feet = 0.9144 m; 1 mile = 1,609.344 m.
- Weight (mass): 1 pound = 0.45359237 kg exactly; 1 ounce = 1/16 pound = 28.349523125 g; 1 stone = 14 pounds.
- Volume: 1 US gallon = 3.785411784 litres and 1 UK (imperial) gallon = 4.54609 litres. A US fluid ounce is 1/128 of a US gallon (about 29.57 ml), and a UK fluid ounce is 1/160 of a UK gallon (about 28.41 ml).
- Temperature: °F = °C × 9/5 + 32, and K = °C + 273.15.
For length, weight and volume the method is always the same: multiply by the size of one "from" unit expressed in the "to" unit. Temperature is different, because the scales start at different zero points, so it uses the formulas above instead of a single multiplier.
Worked examples
- Inches to cm: 13 in × 2.54 = 33.02 cm. A 20 inch tote is 20 × 2.54 = 50.8 cm.
- Cm to inches: divide by 2.54. 45 cm ÷ 2.54 = 17.72 in, which is 17 11/16 in to the nearest sixteenth of an inch, or about 17 3/4 in to the nearest quarter.
- Height in feet and inches: 170 cm ÷ 2.54 = 66.93 in = 5 ft 6.93 in.
- Kg to pounds: 1.2 kg ÷ 0.45359237 = 2.65 lb, or 2 lb 10.33 oz.
- Oven temperature: 180 °C × 9/5 + 32 = 356 °F.
Quick reference: centimetres and inches
| Centimetres | Inches |
|---|---|
| 1 cm | 0.3937 in |
| 2.54 cm | 1 in |
| 5 cm | 1.9685 in |
| 10 cm | 3.937 in |
| 15 cm | 5.9055 in |
| 20 cm | 7.874 in |
| 25 cm | 9.8425 in |
| 30 cm | 11.811 in |
| 30.48 cm | 12 in |
| 50 cm | 19.685 in |
| 100 cm | 39.3701 in |
Quick reference: grams, kilograms, ounces and pounds
| Amount | Equals |
|---|---|
| 100 g | 3.53 oz |
| 250 g | 8.82 oz |
| 500 g | 1.1 lb (1 lb 1.64 oz) |
| 1 kg | 2.2 lb (2 lb 3.27 oz) |
| 2 kg | 4.41 lb |
| 1 oz | 28.35 g |
| 1 lb | 453.59 g |
| 5 lb | 2.27 kg |
Values in the tables are rounded to two to four decimal places. Use the converter above when you need more precision.
US and UK measures are not the same
Pounds, ounces, inches and feet are the same in the US and the UK. Volume is where they differ. A US gallon is about 3.79 litres while a UK gallon is about 4.55 litres, and a US pint is 16 US fluid ounces while a UK pint is 20 UK fluid ounces. Recipes add another twist: the cup in this converter is the US customary cup of 8 US fluid ounces (about 236.6 ml), while nutrition labels in the US use a rounded 240 ml cup and many other countries use a 250 ml metric cup. If a recipe or a product label does not say which system it uses, check before converting.
Tips for sellers listing product sizes
If you sell online to buyers in several countries, show measurements in both systems, for example "13 in (33 cm) wide". Measure the item itself, not the packaging, for the listing, and record the packed size and weight separately for postage. Round sensibly: a bag is fine to the nearest half centimetre or quarter inch, while jewellery and small parts may need millimetres. Our guide on converting cm to inches and kg to lbs explains rounding and labelling in more detail, and the guide to pricing Etsy shipping shows why accurate package weights matter.
Sources
Want the full explanation? Read our guide: How to convert cm to inches and kg to lbs (metric vs imperial).
More guides on this topic:
Frequently asked questions
How many centimetres are in an inch?
Exactly 2.54. Since 1959 the inch has been defined as 25.4 millimetres, so to change inches to centimetres multiply by 2.54, and to change centimetres to inches divide by 2.54.
How do I convert kg to pounds?
Divide the kilograms by 0.45359237, or multiply by about 2.2046. For example, 2 kg is about 4.41 lb. The converter also shows the result as whole pounds plus ounces.
Why are US and UK gallons and pints different?
The two systems kept different historic definitions. A US gallon is 3.785411784 litres and a UK (imperial) gallon is 4.54609 litres. Inches, feet, pounds and ounces are the same in both countries.
How do I convert Celsius to Fahrenheit?
Multiply the Celsius temperature by 9/5 (or 1.8) and add 32. For example, 20 °C × 1.8 + 32 = 68 °F. To go the other way, subtract 32 and multiply by 5/9.
Are my values saved or sent anywhere?
No. The converter runs entirely in your browser. The numbers you type are not sent to our server or stored.