Unit Converter

How conversions work

For length, weight, volume, area, and speed, every unit is converted through a common base unit (meters, kilograms, liters, square meters, or meters/second) using a fixed multiplication factor, so any two units in the same category can be compared directly.

Temperature is different because Celsius, Fahrenheit, and Kelvin scales don't share a common zero point, so each conversion uses its own formula rather than a simple multiplier.

How to use this calculator

Pick a measurement type first (length, weight, volume, area, speed, or temperature), then choose the unit you're converting from and the unit you want. The result updates as you type — there's no separate submit step needed.

Metric vs. imperial

Metric units (meters, kilograms, liters) are the standard almost everywhere outside the US, and are also the base system used in science and engineering worldwide. Imperial and US customary units (miles, pounds, gallons, feet) remain standard for everyday use in the United States, and imperial units still appear in a few specific UK contexts (miles for road distances, for example, even though the UK otherwise uses metric).

Common conversions

• 1 mile ≈ 1.60934 kilometers
• 1 kilogram ≈ 2.20462 pounds
• 1 US gallon ≈ 3.78541 liters
• 0°C = 32°F = 273.15 K
• 1 acre ≈ 43,560 square feet ≈ 4,047 square meters
• 1 hectare ≈ 2.471 acres
• 100 km/h ≈ 62.14 mph
• 1 knot ≈ 1.151 mph (used for wind speed and marine/air navigation)

When you need a more specialised unit

This converter covers everyday length, weight, volume, area, speed and temperature. Recipes that call for teaspoons or cups, shoe and clothing sizes, very large astronomical distances, and engineering quantities such as acceleration, frequency, illuminance and viscosity each have their own converter — they are linked under Related calculators below.

Worked examples

5 miles is 8.0467 kilometers. 150 pounds is 68.0388 kilograms, and 8 ounces is 226.796 grams. 60 mph is 96.5606 km/h, and 1 knot is 1.1508 mph.

Temperature: 72°F is 22.2222 Celsius, 100°C is 373.15 Kelvin and −40°F is −40 Celsius, the point where the two scales meet.

Volume uses a 240 mL cup, so 2 cups is 480 milliliters. The US customary cup is about 236.6 mL, so for recipes use the Cooking Measurement Converter.

How the numbers are displayed

• Results show up to four decimals with trailing zeros removed, so 0.001 grams is not padded to 0.0010.
• A result smaller than 0.00005 shows as 0. 1 milligram in kilograms (0.000001) reads 0 Kilograms, and 0.00001 mm in kilometers also reads 0. Convert to a smaller unit, such as 1 mg to 0.001 g, to see it.
• The factors are rounded values, so some results are slightly off exact figures. 1 mile reads 1609.34 meters (the exact value is 1609.344), and 2.5 acres reads 108900.1432 square feet instead of exactly 108,900.
• Extremely large numbers can appear in exponent form. 1e20 km in millimeters reads 9.999999999999999e+25.

What the tool does not check

Negative values are accepted: −3 km is −3000 meters. Temperatures are not checked against absolute zero either, so −5 Kelvin converts to −278.15 Celsius. An empty box shows "Enter a number to convert."