This chart lists the metric-to-imperial conversions people need most, with the exact factor for each and a shortcut for doing it in your head. Multiply the metric value by the factor to get the imperial or US value, or use the right-hand table to go the other way. Lengths and weights are the same in the US and UK. Volumes aren’t, so US and UK measures are listed separately.
Factors come from NIST SP 811 and the UK Weights and Measures Act 1985. Where a factor is exact by definition, it’s marked.
Length #
| Metric to imperial | Multiply by | Imperial to metric | Multiply by | |
|---|---|---|---|---|
| mm to inches | 0.03937 | inches to mm | 25.4 (exact) | |
| cm to inches | 0.3937 | inches to cm | 2.54 (exact) | |
| m to feet | 3.28084 | feet to m | 0.3048 (exact) | |
| m to yards | 1.09361 | yards to m | 0.9144 (exact) | |
| km to miles | 0.621371 | miles to km | 1.609344 (exact) | |
| km to nautical miles | 0.539957 | nautical miles to km | 1.852 (exact) |
A meter is 3.37 inches longer than a yard, and a 30 cm ruler is just under a foot (11.81 inches).
Weight (mass) #
| Metric to imperial | Multiply by | Imperial to metric | Multiply by | |
|---|---|---|---|---|
| g to ounces | 0.035274 | ounces to g | 28.349523125 (exact) | |
| kg to pounds | 2.20462 | pounds to kg | 0.45359237 (exact) | |
| kg to stone | 0.157473 | stone to kg | 6.35029318 (exact) | |
| tonnes to US short tons | 1.10231 | US short tons to tonnes | 0.90718474 (exact) | |
| tonnes to UK long tons | 0.984207 | UK long tons to tonnes | 1.0160469088 (exact) |
For body weight, luggage and pounds-and-ounces tables, see kg to lbs.
Volume: US measures #
| Metric to US | Multiply by | US to metric | Multiply by | |
|---|---|---|---|---|
| mL to US fluid ounces | 0.033814 | US teaspoons to mL | 4.92892 | |
| mL to US teaspoons | 0.202884 | US tablespoons to mL | 14.7868 | |
| L to US cups | 4.22675 | US fluid ounces to mL | 29.5735 | |
| L to US pints | 2.11338 | US cups to mL | 236.588 | |
| L to US quarts | 1.05669 | US pints to L | 0.473176 | |
| L to US gallons | 0.264172 | US gallons to L | 3.785411784 (exact) |
Volume: UK imperial measures #
| Metric to UK | Multiply by | UK to metric | Multiply by | |
|---|---|---|---|---|
| mL to UK fluid ounces | 0.035195 | UK fluid ounces to mL | 28.4130625 (exact) | |
| L to UK pints | 1.75975 | UK pints to L | 0.56826125 (exact) | |
| L to UK gallons | 0.219969 | UK gallons to L | 4.54609 (exact) |
A UK gallon is 20% bigger than a US gallon, and a UK pint is 568 mL against the US pint’s 473 mL. See US gallon vs imperial gallon for why.
Area #
| Metric to imperial | Multiply by | Imperial to metric | Multiply by | |
|---|---|---|---|---|
| cm² to square inches | 0.155 | square inches to cm² | 6.4516 (exact) | |
| m² to square feet | 10.7639 | square feet to m² | 0.09290304 (exact) | |
| m² to square yards | 1.19599 | square yards to m² | 0.83612736 (exact) | |
| hectares to acres | 2.47105 | acres to hectares | 0.40468564224 (exact) | |
| km² to square miles | 0.386102 | square miles to km² | 2.58999 |
An acre is 43,560 square feet. A 2,000-square-foot house is 185.8 m², and a 50 m² apartment is 538 square feet.
Temperature #
Temperature uses formulas, not a single factor, because the scales start at different zeros:
| Conversion | Formula | Check |
|---|---|---|
| °C to °F | °F = °C × 1.8 + 32 | 100 °C = 212 °F |
| °F to °C | °C = (°F − 32) ÷ 1.8 | 32 °F = 0 °C |
| °C to K | K = °C + 273.15 | 0 °C = 273.15 K |
Charts for weather, body and oven temperatures are in Celsius to Fahrenheit formula.
Speed, pressure, energy and fuel #
| Conversion | Multiply by |
|---|---|
| km/h to mph | 0.621371 |
| mph to km/h | 1.609344 (exact) |
| m/s to km/h | 3.6 (exact) |
| knots to mph | 1.15078 |
| bar to psi | 14.5038 |
| psi to kPa | 6.89476 |
| kPa to psi | 0.145038 |
| kJ to kcal (food Calories) | 0.239006 |
| kcal to kJ | 4.184 (exact) |
| kWh to BTU | 3,412.14 |
| kW to horsepower (mechanical) | 1.34102 |
| US mpg to L/100km | 235.215 ÷ mpg |
| UK mpg to L/100km | 282.481 ÷ mpg |
Fuel economy divides instead of multiplying because mpg and L/100km are reciprocals: more miles per gallon means fewer liters per 100 km. Divide the constant by your figure, so 30 US mpg is 235.215 ÷ 30 = 7.84 L/100km.
Mental shortcuts and how close they are #
| Conversion | Shortcut | Error |
|---|---|---|
| inches to cm | × 2.5 | 1.6% low |
| m to feet | × 3.3 | 0.6% high |
| km to miles | × 5/8 | 0.6% high |
| miles to km | × 1.6 | 0.6% low |
| kg to lb | double, then add 10% | 0.2% low |
| g to oz | × 0.035 | 0.8% low |
| L to US gallons | × 0.26 | 1.6% low |
| mL to US fl oz | ÷ 30 | 1.4% low |
| m² to square feet | × 10.8 | 0.3% high |
| hectares to acres | × 2.5 | 1.2% high |
| bar to psi | × 14.5 | under 0.1% |
| °C to °F | double, subtract 10%, add 32 | exact |
How to use this chart #
Multiply by the factor in the row that matches your direction. Don’t divide by the factor from the other side unless you check it’s the exact reciprocal. For example, “kg to pounds” (2.20462) and “pounds to kg” (0.45359237) are reciprocals, but one is rounded and one is exact, so going through the exact one keeps your answer precise.
For square and cubic units, the factors are already squared or cubed. Using the plain length factor for an area is the most common conversion mistake. We walk through why, with examples, in how to convert units.
To print just the tables, use your browser’s print preview and select the pages you need.
Doing it on your phone #
Convert Units Calculator uses the same exact definitions as this chart, works offline and shows the whole category at once, so one entry gives you every row of a table like the ones above. Version 1.0.5 covers 19 categories, including area, pressure, energy, power and fuel economy, with US and UK volumes listed separately.
Frequently asked questions #
What is the metric to imperial conversion for length? #
The key factors are 1 inch = 2.54 cm, 1 foot = 0.3048 m, 1 yard = 0.9144 m and 1 mile = 1.609344 km, all exact. Going the other way, 1 m is 3.28084 feet and 1 km is 0.621371 miles.
Is imperial the same as US customary? #
For length and weight, yes: they’ve been identical since 1959. For volume, no. US and UK gallons, quarts, pints and fluid ounces are different sizes, so check which system your source uses.
Which conversion factors are exact? #
Those that come from a definition: 1 inch = 2.54 cm, 1 pound = 0.45359237 kg, 1 US gallon = 3.785411784 L, 1 UK gallon = 4.54609 L, and anything derived from them, such as the foot, yard, mile, ounce and square foot. Their reciprocals (like 2.20462 lb per kg) never end, so they’re always rounded.
How do you convert square meters to square feet? #
Multiply by 10.7639. A 20 m² room is 215.3 square feet. Going the other way, multiply square feet by 0.09290304.
What’s the easiest way to remember metric conversions? #
Learn a few anchors: an inch is 2.5 cm, a meter is a bit over 3 feet, a kilometer is about 5/8 of a mile, a kilogram is about 2.2 pounds, and a liter is a bit more than a US quart. The shortcut table above shows how far off each one is.