Unit Converter
Convert between metric and imperial units; length, area, volume, weight, and temperature instantly.
Unit Converter
Select a category, choose units, and type a value to convert.
How Does the Formula Work?
This unit converter covers five categories: length, area, volume, weight and temperature. Type a number in either field and the other one updates as you type; there is no button to press.
Temperature: °F = °C × 9/5 + 32 | °C = (°F − 32) × 5/9 | K = °C + 273.15
Length, area, volume and weight go through a base unit (meter, square meter, cubic meter, kilogram), and every factor is the defined value rather than a rounded one. Temperature uses the formulas above instead, because its scales start from different zero points.
Key Relationships
Key relationships: 1 inch = 2.54 cm (exact), 1 foot = 30.48 cm, 1 mile = 1.609 km, 1 pound = 0.4536 kg, 1 gallon (US) = 3.785 liters, 1 acre = 4,047 m².
Where Conversions Come Up
Construction: feet/inches to meters for international plans. Cooking: US cups to milliliters. Travel: miles to kilometers, Fahrenheit to Celsius. Shipping: pounds to kilograms, cubic feet to cubic meters. Real estate: square feet to square meters, acres to hectares.
Precision and Rounding
Results show up to 2 decimal places from 1 upward, 4 below 1 and 6 below 0.01. Below 0.001 and from 1,000,000,000 upward, the converter switches to scientific notation, written like 1.5e+9 (1.5 × 10⁹), and you can type that form too. For everyday use, 2 decimal places are usually enough; for engineering work, check the precision your project needs.
Two factors are exact by definition, 1 inch = 2.54 cm and 1 pound = 0.45359237 kg, and so is the US gallon, 231 cubic inches. Every other US customary factor here follows from those three, so the converter works with exact values and rounds only what it shows you.
Temperature Reference Points
A few fixed pairs help you sanity-check a result: 0 °C = 32 °F = 273.15 K, 100 °C = 212 °F, 37 °C = 98.6 °F, and -40 °C = -40 °F. If a conversion lands far from these, check that the right units are selected, for example that a Kelvin value has not gone into a Fahrenheit box.
US Customary and British Imperial
US customary units and British imperial units share names but not every value. The biggest gap is in volume: a US gallon is 3.785 liters, while an imperial gallon is 4.546 liters. This converter uses US gallons.
Length Conversion Essentials
Key conversions: 1 inch equals 2.54 centimeters exactly, since 1 July 1959. 1 foot equals 30.48 centimeters. 1 yard equals 0.9144 meters. 1 mile equals 1.609344 kilometers. For a rough figure, 1 meter is about 3.28 feet and 1 kilometer about 0.62 miles.
Area and Volume
Area conversions square the linear factor. Since 1 foot equals 0.3048 meters, 1 square foot equals 0.09290304 square meters. One acre (43,560 square feet) equals 0.4047 hectares. Volume conversions cube it: 1 cubic foot equals 0.0283 cubic meters. Gallons are the easiest to mix up: 1 US gallon equals 3.785 liters, while 1 imperial gallon equals 4.546 liters. For recipes, 1 US cup is 236.59 milliliters, 1 tablespoon 14.79 mL and 1 teaspoon 4.93 mL.
Weight and Mass
Weight conversions: 1 pound equals 0.4536 kilograms. 1 ounce equals 28.35 grams. 1 stone (14 pounds) equals 6.35 kilograms. 1 metric ton equals 1,000 kilograms, or 2,204.6 pounds. 500 grams is about 1.1 pounds. The troy ounce, 31.1 grams, is a different unit from the ordinary (avoirdupois) ounce of 28.35 grams that this converter uses.
Temperature
Celsius and Fahrenheit are linked by a straight-line formula with an offset: F equals C times 9 divided by 5, plus 32. Because of the offset, 0 °C is not 0 °F, and doubling a Celsius temperature does not double its Fahrenheit value. Water freezes at 0 degrees Celsius, which is 32 degrees Fahrenheit, and 100 °C is 212 °F. The two scales read the same at minus 40 degrees. For a dedicated temperature tool with Kelvin and Rankine support use our Temperature Converter.
When You Need Conversions
Unit conversions come up in travel, online shopping from foreign retailers, recipes from other countries, scientific work, engineering projects with international specifications, imported building materials and shipping weights. The SI units themselves are defined by the International Bureau of Weights and Measures (BIPM), and the National Institute of Standards and Technology (NIST) lists the conversion factors for US customary units in its Guide to the SI (Special Publication 811).
Tips & Recommendations
Type in either field; the other updates automatically. No need to click Convert.
Click ⇄ to swap the from/to units and values instantly.
Switch between length, area, volume, weight, and temperature using the tabs.
Up to 6 decimal places for small values; scientific notation below 0.001 and from one billion up.
Frequently Asked Questions
How many cm in an inch?
1 inch = 2.54 cm, exactly. The value has been fixed since 1 July 1959, when the English-speaking countries settled on one yard and one pound defined in metric terms, and every other inch-based length follows from it.
How to convert °F to °C?
Subtract 32, then multiply by 5/9. Example: 72°F → (72−32) × 5/9 = 22.2°C. Quick mental math: for a rough estimate, subtract 30 and divide by 2. This gives 72°F → (72−30)/2 = 21°C, which is close to the exact 22.2°C.
US vs UK gallon?
US = 3.785 L. UK (Imperial) = 4.546 L. This converter uses US gallons.
How many ft² in an acre?
1 acre = 43,560 square feet = 4,047 square meters = 0.4047 hectares.
How many lb in a kg?
1 kilogram = 2.2046 pounds. Conversely, 1 pound = 0.4536 kilograms. For a quick estimate, multiply kg by 2.2 or divide lb by 2.2.