Unit Converter: Length, Weight, Temperature and More
Pick a category and two units to convert a value, for example meters to feet or Celsius to Fahrenheit.
Convert units of measurement: exact factors and examples
Each unit is defined by a factor relative to its category’s base unit (metre for length, kilogram for mass…): converted value = value × source factor ÷ target factor. So 1 m equals 1 ÷ 0.3048 = 3.28084 feet, the foot being exactly 0.3048 m. For distances, a mile is exactly 1.609344 km, so 1 km = 0.621371 mi; the table below lists common values and race distances.
The method
When the page opens, it converts 10 km to miles: 10 × 1,000 ÷ 1,609.344 = 6.213712 mi. The rounded answer, 10 km = 6.21 mi, appears at the top, and while the conversion is between km and miles, a table under the result gives 1, 5 and 10 km, the half marathon and the marathon in miles, then 1, 5, 10 and 26.2 miles in km. For 1 metre in feet: 1 × 1 ÷ 0.3048 = 3.28084 ft. Temperatures are not proportional and go through degrees Celsius: °C = (°F − 32) × 5/9, K = °C + 273.15, °R (Rankine) = (°C + 273.15) × 9/5, °Ré (Réaumur) = °C × 4/5. 100 °F gives 37.777778 °C.
Km to miles and miles to km table
The international mile, set by the 1959 international yard and pound agreement, is 5,280 feet of 0.3048 m, exactly 1.609344 km, so 1 km is 0.621371 mi. Values are rounded to three decimals; the converter shows six.
| Kilometres to miles | Miles to kilometres |
|---|---|
| 1 km = 0.621 mi | 1 mi = 1.609 km |
| 2 km = 1.243 mi | 2 mi = 3.219 km |
| 3 km = 1.864 mi | 3 mi = 4.828 km |
| 4 km = 2.485 mi | 4 mi = 6.437 km |
| 5 km = 3.107 mi | 5 mi = 8.047 km |
| 6 km = 3.728 mi | 6 mi = 9.656 km |
| 7 km = 4.350 mi | 7 mi = 11.265 km |
| 8 km = 4.971 mi | 8 mi = 12.875 km |
| 9 km = 5.592 mi | 9 mi = 14.484 km |
| 10 km = 6.214 mi | 10 mi = 16.093 km |
| 15 km = 9.321 mi | 15 mi = 24.140 km |
| 20 km = 12.427 mi | 20 mi = 32.187 km |
| 25 km = 15.534 mi | 25 mi = 40.234 km |
| 30 km = 18.641 mi | 30 mi = 48.280 km |
| 40 km = 24.855 mi | 40 mi = 64.374 km |
| 50 km = 31.069 mi | 50 mi = 80.467 km |
| 100 km = 62.137 mi | 100 mi = 160.934 km |
Road race distances:
| Race | Kilometres | Miles |
|---|---|---|
| 5K | 5 km | 3.107 mi |
| 10K | 10 km | 6.214 mi |
| Half marathon | 21.0975 km | 13.109 mi |
| Marathon | 42.195 km | 26.219 mi |
Exact factors used
- Inch = 0.0254 m, foot = 0.3048 m, yard = 0.9144 m, mile = 1,609.344 m, nautical mile = 1,852 m.
- Pound = 0.45359237 kg, ounce = 28.349523125 g, troy ounce = 31.1034768 g, carat = 0.2 g.
- US gallon = 3.785411784 L, imperial gallon = 4.54609 L, acre = 4,046.8564224 m².
- Calorie = 4.184 J, kWh = 3.6 MJ, atmosphere = 1.01325 bar, astronomical unit = 149,597,870,700 m.
Decimal and binary bytes
The tool separates decimal prefixes (1 GB = 1,000 MB) from binary ones (1 GiB = 1,024 MiB = 1,073.741824 MB). A drive sold as 1 TB therefore shows about 0.909 TiB on a system that counts in binary.
Display and limits
Results are rounded to 6 decimals; above 109 or below 0.0001 they switch to scientific notation (5e-5). A year is 365 days but the average month is 30.4375 days (365.25 ÷ 12), so twelve months make 1.000685 years. Mach is fixed at 1,234.8 km/h, the speed of sound in air at about 20 °C, although it varies with temperature. Cooking cups and spoons are customary measures, not legal units.
Sources and dates: SI units and prefixes from the BIPM SI Brochure, 9th edition (2019), updated in 2026; international foot fixed at exactly 0.3048 m since 1959, US survey foot retired after 31/12/2022: NIST, Ending the Era of the U.S. Survey Foot (checked 14/10/2026); marathon (42.195 km, 26 miles 385 yards) and half marathon (21.0975 km) distances: World Athletics, Marathon and Half Marathon pages (checked 22/10/2026).
Frequently Asked Questions
How many centimetres are in an inch?
An inch is exactly 2.54 cm. This follows from the international foot of 0.3048 m adopted in 1959 (one foot = 12 inches). A 27-inch screen therefore has a 68.58 cm diagonal.
How do I convert Fahrenheit to Celsius?
Subtract 32, then multiply by 5/9: 100 °F = (100 − 32) × 5/9 = 37.8 °C. The other way, °F = °C × 9/5 + 32, so 100 °C is 212 °F.
What is the difference between a GB and a GiB?
A gigabyte (GB) counts in powers of 10: 1,000,000,000 bytes. A gibibyte (GiB) counts in powers of 2: 1,073,741,824 bytes, about 7.4% more. That is why a 500 GB drive shows roughly 465 GiB.
How many kilometres are in a mile?
An international mile is exactly 1.609344 km, and one kilometre is 0.621371 miles. The nautical mile used at sea and in aviation is longer: 1.852 km.
Is this tool really free?
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