Imperial to Metric Conversion Calculator
Convert imperial to metric (and back) instantly: inches to cm, feet to meters, miles to km, pounds to kg, ounces to grams, Fahrenheit to Celsius, gallons to liters. Every factor used here is the exact internationally defined value, so conversions round-trip perfectly. 100% client-side: nothing you type ever leaves your browser.
Temperature uses an offset formula, not a multiply factor: select the direction above.
Popular conversions
Metric conversion chart: quick reference tables
Length: imperial to metric
| Imperial | Metric (exact) | Reverse |
|---|---|---|
| 1 inch (in) | 2.54 cm | 1 cm = 0.393701 in |
| 1 foot (ft) | 30.48 cm | 1 m = 3.28084 ft |
| 1 yard (yd) | 0.9144 m | 1 m = 1.09361 yd |
| 1 mile (mi) | 1.609344 km | 1 km = 0.621371 mi |
Need a combined feet-and-inches entry (e.g. 5 ft 9 in)? Use our feet and inches to cm converter.
Weight: imperial to metric
| Imperial | Metric (exact) | Reverse |
|---|---|---|
| 1 ounce (oz) | 28.3495 g | 1 g = 0.035274 oz |
| 1 pound (lb) | 0.45359237 kg | 1 kg = 2.20462 lb |
| 1 stone (st) | 6.35029 kg | 1 kg = 0.157473 st |
| 1 US ton | 907.1847 kg | 1 t = 1.10231 US tons |
| 1 imperial ton | 1016.0469 kg | 1 t = 0.984207 imperial tons |
Also try the dedicated kg to pounds converter.
Volume: imperial to metric
| Imperial | Metric (exact) | Reverse |
|---|---|---|
| 1 US fluid ounce | 29.5735 mL | 1 mL = 0.033814 US fl oz |
| 1 imperial fluid ounce | 28.4131 mL | 1 mL = 0.0351951 imperial fl oz |
| 1 US gallon | 3.78541 L | 1 L = 0.264172 US gal |
| 1 imperial gallon | 4.54609 L | 1 L = 0.219969 imperial gal |
Temperature: Fahrenheit to Celsius anchors
| Fahrenheit | Celsius | Common reference |
|---|---|---|
| -40 °F | -40 °C | scales meet |
| 0 °F | -17.78 °C | |
| 32 °F | 0 °C | water freezes |
| 68 °F | 20 °C | room temperature |
| 98.6 °F | 37 °C | body temperature |
| 212 °F | 100 °C | water boils |
How to convert imperial to metric
Length
Multiply by the exact factor: inches to cm is inches × 2.54, inches to mm is inches × 25.4, feet to meters is feet × 0.3048, yards to meters is yards × 0.9144, miles to km is miles × 1.609344. To go the other way, divide by the same factor (for example, cm ÷ 2.54 = inches).
Weight
Multiply: ounces to grams is ounces × 28.349523125, pounds to kg is pounds × 0.45359237, stones to kg is stones × 6.35029318. US tons and imperial tons differ: a US ton is 2,000 lb (907.18474 kg) while an imperial ton is 2,240 lb (1016.0469088 kg).
Volume
Multiply: gallons to liters (US) is US gallons × 3.785411784, imperial gallons × 4.54609, and fl oz to ml is US fl oz × 29.5735295625 (imperial fl oz × 28.4130625). Check which fluid ounce and gallon your source uses, the US and imperial versions are not interchangeable.
Temperature
Use the offset formulas: °C = (°F − 32) × 5/9 and °F = °C × 9/5 + 32. Unlike the other categories, temperature needs an offset (32) because the two scales start at different zeros.
US gallon vs imperial gallon
This is the single most common source of conversion errors. The US gallon (3.785411784 L) is defined as 231 cubic inches, while the imperial gallon (4.54609 L) was defined in 1824 as the volume occupied by 10 pounds of water. The imperial gallon is about 20% larger than the US gallon. The same split applies to fluid ounces: a US fluid ounce is 1/128 of a US gallon (29.5735 mL), while an imperial fluid ounce is 1/160 of an imperial gallon (28.4131 mL). The converter above keeps both systems as separate units so you never mix them up.
Why the conversion factors are exact
The inch and the pound are no longer defined by physical artifacts. The international yard and pound agreement of 1959 fixed 1 inch = 2.54 cm and 1 pound = 0.45359237 kg exactly, which is why inches to cm and pounds to kg conversions have zero definitional error. The US gallon is exactly 231 cubic inches by US law, giving exactly 3.785411784 liters; the imperial gallon is exactly 4.54609 liters by UK definition. This page uses the full exact factors in every calculation and only rounds what is shown on screen, so converting A to B and back to A returns the original value.
Privacy
All conversions run locally in your browser with JavaScript. Nothing you type is uploaded, stored, or sent anywhere. The page works offline once loaded. There are no accounts, no tracking cookies, and no ads inside the tool.
Frequently asked questions
What is imperial to metric conversion?
How many centimeters are in an inch?
How many kilograms are in a pound?
How do I convert Fahrenheit to Celsius?
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How many liters are in a gallon?
How many grams are in an ounce?
How many kilograms are in a stone?
Are these conversion factors exact or rounded?
How many miles are in a kilometer?
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