Every factor uses the exact international definition - the inch is exactly 25.4 mm, the pound exactly 0.45359237 kg. Results update in both directions as you type.
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How unit conversion works
Every conversion between two units of the same kind is a single multiplication: value × conversion factor. To convert 5 miles to kilometers, multiply by 1.609344 (the exact definition of a mile in kilometers): 5 × 1.609344 = 8.04672 km. Going the other way uses the reciprocal - divide by the same factor.
The one exception is temperature, because the scales don't share a zero point - converting needs an offset as well as a factor:
| Conversion | Formula |
|---|---|
| Celsius → Fahrenheit | °F = °C × 9/5 + 32 |
| Fahrenheit → Celsius | °C = (°F − 32) × 5/9 |
| Celsius → Kelvin | K = °C + 273.15 |
| Kelvin → Celsius | °C = K − 273.15 |
Common conversion tables
The pairs people look up most, precomputed. For anything else, use the converter above.
Centimeters to inches
| cm | inches |
|---|---|
| 1 | 0.3937 |
| 2 | 0.7874 |
| 5 | 1.9685 |
| 10 | 3.9370 |
| 15 | 5.9055 |
| 20 | 7.8740 |
| 30 | 11.8110 |
| 50 | 19.6850 |
| 100 | 39.3701 |
Kilograms to pounds
| kg | pounds |
|---|---|
| 1 | 2.2046 |
| 2 | 4.4092 |
| 5 | 11.0231 |
| 10 | 22.0462 |
| 20 | 44.0925 |
| 50 | 110.2311 |
| 75 | 165.3467 |
| 100 | 220.4623 |
Miles to kilometers
| miles | km |
|---|---|
| 1 | 1.609 |
| 3 | 4.828 |
| 5 | 8.047 |
| 10 | 16.093 |
| 13.1 (half marathon) | 21.082 |
| 26.2 (marathon) | 42.165 |
| 50 | 80.467 |
| 100 | 160.934 |
Celsius to Fahrenheit
| °C | °F |
|---|---|
| −40 | −40 |
| −10 | 14 |
| 0 | 32 |
| 10 | 50 |
| 20 | 68 |
| 25 | 77 |
| 30 | 86 |
| 37 | 98.6 |
| 100 | 212 |
Frequently asked questions
How do I convert centimeters to inches?
Divide the length in centimeters by 2.54. One inch is defined as exactly 2.54 centimeters, so 10 cm ÷ 2.54 = 3.937 inches. To go the other way, multiply inches by 2.54.
How many kilograms are in a pound?
One pound is defined as exactly 0.45359237 kilograms, so a kilogram is about 2.2046 pounds. Quick mental math: double the kilograms and add 10% to get pounds (70 kg → 140 + 14 = 154 lb, exact answer 154.32).
What is the formula to convert Celsius to Fahrenheit?
°F = °C × 9/5 + 32. For example, 20 °C × 9/5 = 36, plus 32 gives 68 °F. Going the other way: °C = (°F − 32) × 5/9. The two scales meet at −40°, which is the same temperature in both.
Why is there no currency converter?
Deliberately. Exchange rates change by the minute and would require fetching live data from a server - and this tool's promise is that it makes no network requests at all and works fully offline. Physical units never change, so every conversion here is exact and permanent.
What is the difference between US and imperial gallons?
A US gallon is 3.785 liters; an imperial (UK) gallon is 4.546 liters - about 20% bigger. The same split affects pints, quarts, and fluid ounces. This converter labels US and imperial units separately so recipes and fuel economy figures don't get silently mistranslated.
What is the difference between a kilobyte (kB) and a kibibyte (KiB)?
A kilobyte is 1,000 bytes (decimal, used by drive manufacturers and networking); a kibibyte is 1,024 bytes (binary, used by operating systems for memory). The gap compounds: a terabyte is 10¹² bytes but a tebibyte is about 10% more. It is why a "1 TB" drive shows up as roughly 931 "GB" in Windows - Windows is actually displaying gibibytes.
How accurate are the conversions?
Exact, up to floating-point precision (about 15 significant digits). Every factor uses the exact international definition - the inch is exactly 25.4 mm, the pound exactly 0.45359237 kg, the standard atmosphere exactly 101,325 Pa. The only approximations are inherently average units, like the month and year, which are marked as such.
Does the unit converter work offline?
Yes. All conversion tables are built into the page and the math runs in your browser, so once loaded it works with no connection - nothing you type is ever sent anywhere. Save the page to your device and it works forever.