Unit Converter
Convert length, mass, temperature, volume and speed.
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What is the Unit Converter?
Unit conversion comes up constantly: following a recipe written in US fluid ounces, reading a running distance in kilometers, checking a package weight in pounds for shipping, or converting a weather report from Celsius. Errors are common because some conversions are simple multiplication while temperature needs an offset, and because units like the gallon have different US and imperial definitions.
This converter covers five measurement families. Length: meters, kilometers, feet and miles. Mass: kilograms, grams, pounds and ounces. US liquid volume: liters, milliliters, US gallons and US fluid ounces. Speed: meters per second, kilometers per hour, miles per hour and knots. Temperature: Celsius, Fahrenheit and kelvin. Non-temperature values are converted through a base unit using exact defined factors where they exist, such as 0.3048 m per foot and 0.45359237 kg per pound. Results are shown to nine significant digits, and temperatures below absolute zero are rejected. Everything runs in your browser.
How to use it
- 1Choose a measurement family.
- 2Enter the source value and units.
- 3Read the converted value.
How it works
Each measurement family uses fixed conversion factors into a base unit; temperature uses its offset formula.
Example
Convert 5 kilometers to 3.10686 miles, or 25 °C to 77 °F.
Limitations & notes
- Conversions are rounded for display.
- US customary and imperial volume units are different; this tool uses US liquid volume.
Frequently asked questions
How do I convert Celsius to Fahrenheit by hand?
Multiply the Celsius value by 9/5 (or 1.8) and add 32. For example, 25 °C × 1.8 = 45, plus 32 gives 77 °F. To go the other way, subtract 32 and multiply by 5/9: 98.6 °F becomes 37 °C. Kelvin is Celsius plus 273.15, so 0 °C is 273.15 K. The converter applies these same formulas and refuses inputs below absolute zero, which is −273.15 °C or −459.67 °F.
Is a US gallon the same as a UK gallon?
No. A US liquid gallon is exactly 3.785411784 liters, while an imperial (UK) gallon is 4.54609 liters, about 20 percent larger. US and imperial fluid ounces also differ. This tool uses US liquid units only, so 1 US gal shows as 3.78541178 L. If a recipe or fuel figure comes from the UK, convert using the imperial definition instead of these results.
How many feet are in a mile and kilometers in a mile?
A mile is 5,280 feet and exactly 1,609.344 meters, so it is about 1.609 kilometers. In the other direction, 1 kilometer is about 0.621 miles, which is why a 5K race is roughly 3.1 miles and a 10K is about 6.2 miles. A foot is defined as exactly 0.3048 meters. The converter uses these exact definitions as its factors.
What is a knot and how does it compare to mph?
A knot is one nautical mile per hour, and a nautical mile is 1,852 meters. One knot therefore equals about 1.151 mph, 1.852 km/h or 0.5144 meters per second. Knots are standard in aviation and marine weather, so a reported wind of 20 knots is about 23 mph. This tool uses 0.514444 m/s per knot, accurate to about six digits.
Can this tool convert cooking cups, stone or nautical miles?
Not directly. The converter covers only the units listed in each family: m, km, ft and mi for length; kg, g, lb and oz for mass; L, mL, US gal and US fl oz for volume; m/s, km/h, mph and knots for speed; and °C, °F and K for temperature. For cups, one US cup is 8 US fluid ounces, so you can convert the fluid ounce value and divide by eight.
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