To convert metric to imperial, multiply by the unit’s conversion factor: kilometres × 0.621 = miles, kilograms × 2.205 = pounds, and °C × 9/5 + 32 = °F.
Whether you are following an American recipe in a metric kitchen, reading a European road sign, or checking your weight abroad, knowing how to convert metric to imperial units saves confusion and mistakes. The two systems, metric with its metres, grams, and litres, and imperial with its feet, pounds, and gallons, describe the same quantities in different languages. Converting between them is just multiplication by the right factor, and there is a tidy method, called dimensional analysis, that makes it foolproof by letting the units cancel out. This guide gives you that method, a table of the conversions you will actually use, worked examples including the trickier temperature case, and a warning about the rounding errors that catch people out. Our unit converter handles any conversion instantly; here is how it works.
The two systems
The metric system, used by most of the world, is built on units of ten: millimetres, centimetres, metres, and kilometres for length; grams and kilograms for weight; millilitres and litres for volume. Its consistency makes it easy to scale up and down.
The imperial and closely related US customary systems use inches, feet, miles, ounces, pounds, and gallons. They are still standard in the United States and appear in the United Kingdom for some everyday measures. Converting between the two is a matter of applying the correct factor, which is where a reliable method helps.
The dimensional analysis method
The cleanest way to convert is to multiply by the conversion factor written as a fraction, arranged so the unit you are leaving cancels out.
value x (target unit / original unit) = converted value
For example, to convert 5 miles to kilometres, multiply by 1.609 km per 1 mile: 5 miles x (1.609 km / 1 mile) = 8.05 km. The word mile cancels, leaving kilometres. Writing it this way stops you accidentally dividing when you should multiply, the most common conversion mistake.
Common conversions table
These are the conversions that cover most everyday needs. Multiply by the factor shown.
| Quantity | Conversion |
|---|---|
| Length | 1 inch = 2.54 cm |
| Length | 1 foot = 30.48 cm |
| Length | 1 mile = 1.609 km |
| Length | 1 metre = 3.281 feet |
| Weight | 1 pound = 0.4536 kg |
| Weight | 1 kilogram = 2.205 pounds |
| Weight | 1 ounce = 28.35 g |
| Volume | 1 US gallon = 3.785 litres |
| Volume | 1 UK gallon = 4.546 litres |
| Volume | 1 US cup = about 240 ml |
To reverse any conversion, divide instead of multiply, or use the reciprocal factor. For instance, kilograms to pounds multiplies by 2.205; pounds to kilograms multiplies by 0.4536.
Convert anything instantly
Our unit converter covers length, weight, volume, temperature, and more, in both directions. It pairs well with our distance calculator for travel and our volume guide for capacity, and it is a lifesaver when scaling a recipe written in unfamiliar units.
Temperature: the special case
Temperature does not convert with a simple multiplier, because the Celsius and Fahrenheit scales start at different points. You need a formula that both scales and shifts.
Fahrenheit = (Celsius x 9/5) + 32
Celsius = (Fahrenheit – 32) x 5/9
For example, 20 degrees Celsius is (20 x 9/5) + 32 = 36 + 32 = 68 degrees Fahrenheit. Going the other way, 100 degrees Fahrenheit is (100 – 32) x 5/9 = about 37.8 degrees Celsius. The plus-32 step is what makes temperature different from every other conversion in this guide.
Rounding errors and US vs UK units
Two traps cause most conversion errors. The first is rounding too early. Using a rough factor like 1 mile equals 1.6 km is fine for a quick estimate, but over a long distance the small error adds up. For accuracy, use the fuller factor, 1.609, and round only at the end.
The second is assuming US and imperial units are identical. They are not, especially for volume: a US gallon is 3.785 litres while a UK gallon is 4.546 litres, and US and UK pints and fluid ounces differ too. When a recipe or fuel figure uses gallons, always check which gallon is meant, or the conversion can be off by a fifth.
Frequently asked questions
How do I convert metric to imperial?
Multiply the metric value by the appropriate conversion factor. For example, kilometres to miles multiplies by 0.621, and kilograms to pounds by 2.205. The dimensional analysis method, writing the factor as a fraction so the original unit cancels, prevents mistakes. Temperature is the exception, needing a formula that both scales and shifts rather than a single multiplier.
How do I convert miles to kilometres?
Multiply the number of miles by 1.609. So 5 miles is 5 times 1.609, which equals about 8.05 kilometres. To go the other way, from kilometres to miles, multiply by 0.621 instead. For a rough mental estimate you can use 1.6, but for accuracy over long distances use the fuller factor of 1.609 and round at the end.
How do I convert kilograms to pounds?
Multiply the kilograms by 2.205 to get pounds. For example, 10 kilograms is 10 times 2.205, which is about 22.05 pounds. To convert pounds back to kilograms, multiply by 0.4536 instead, so 10 pounds is about 4.54 kilograms. These reciprocal factors let you convert weight in either direction accurately.
How do I convert Celsius to Fahrenheit?
Multiply the Celsius temperature by 9/5, then add 32. So 20 degrees Celsius is 20 times 9/5, which is 36, plus 32, giving 68 degrees Fahrenheit. To reverse it, subtract 32 first, then multiply by 5/9. Temperature needs this two-step formula because the two scales have different starting points, unlike other unit conversions.
Why do US and UK measurements differ?
Although both descend from the old imperial system, the United States standardised slightly different volume units. A US gallon is 3.785 litres while a UK gallon is 4.546 litres, and their pints and fluid ounces differ too. Length and weight units like the inch and pound are the same, but for volume you must always check which country’s unit a figure uses.
What is dimensional analysis for unit conversion?
Dimensional analysis is a method where you multiply a value by a conversion factor written as a fraction, arranged so the original unit cancels and the target unit remains. For example, 5 miles times 1.609 km per mile cancels miles and leaves kilometres. It is reliable because the cancelling units confirm you have set the conversion up the right way round.
The bottom line
Converting metric to imperial is multiplication by the right factor: miles to kilometres times 1.609, kilograms to pounds times 2.205, and so on. The dimensional analysis trick, writing the factor as a fraction so units cancel, keeps you from multiplying when you should divide. Temperature is the one exception, needing the scale-and-shift formula with its plus-32 step. Watch for early rounding and for the real difference between US and UK gallons. For any conversion in either direction, our unit converter gives you the precise answer at once.
Further reading
For authoritative background on this topic, see Conversion of units on Wikipedia.
Note. This article is for general informational purposes. Conversion factors are rounded for readability; for precise or safety-critical work, use full-precision factors and confirm whether US or UK units apply.
Last reviewed: July 2026