Convert between units of length, weight, temperature, volume, speed, and area — instantly as you type.
To convert between metric and imperial units, multiply or divide by the appropriate conversion factor. This converter handles all calculations automatically — just select your units and type a value.
Key conversion factors: 1 inch = 2.54 cm, 1 mile = 1.609 km, 1 pound = 0.4536 kg, 1 gallon (US) = 3.785 liters, 1 acre = 4,047 m². Temperature conversions use formulas rather than simple multiplication: °F = °C × 9/5 + 32, and K = °C + 273.15.
Multiply the Celsius temperature by 9/5 (or 1.8), then add 32. For example, 25°C = (25 × 1.8) + 32 = 77°F. To convert Fahrenheit to Celsius: subtract 32, then multiply by 5/9.
Key reference points: 0°C = 32°F (water freezes), 100°C = 212°F (water boils), 37°C = 98.6°F (body temperature), −40°C = −40°F (the point where both scales meet). Kelvin uses the same increments as Celsius but starts at absolute zero: 0K = −273.15°C.
A US gallon equals 3.785 liters, while an Imperial (UK) gallon equals 4.546 liters — about 20% larger. This converter uses US gallons, which are standard in the United States.
The difference originates from different historical definitions. The US gallon is based on the wine gallon (231 cubic inches), while the Imperial gallon is based on the volume of 10 pounds of water. When converting recipes or fuel economy between US and UK sources, this difference matters significantly.
Whether you're cooking, traveling, or working on a project, these are the unit conversions people search for most frequently.
| Conversion | Factor | Quick Example |
|---|---|---|
| inches → cm | × 2.54 | 12 in = 30.48 cm |
| feet → meters | × 0.3048 | 6 ft = 1.83 m |
| miles → km | × 1.609 | 100 mi = 160.9 km |
| pounds → kg | × 0.4536 | 150 lb = 68 kg |
| ounces → grams | × 28.35 | 8 oz = 226.8 g |
| gallons → liters | × 3.785 | 5 gal = 18.93 L |
| cups → mL | × 236.6 | 2 cups = 473 mL |
| acres → hectares | × 0.4047 | 10 ac = 4.05 ha |
The US is one of only three countries (along with Myanmar and Liberia) that hasn't officially adopted the metric system as its primary measurement standard.
The Metric Conversion Act of 1975 made metric the "preferred" system but adoption was voluntary, and public resistance was strong. The estimated cost of fully converting US road signs, manufacturing, and education was billions of dollars with no immediately obvious benefit to consumers. In practice, the US uses metric extensively in science, medicine, military, and international trade — it's everyday consumer measurements (miles, pounds, Fahrenheit, cups) that remain imperial. The UK is a hybrid: road distances in miles but liquids in liters, body weight in stone/pounds but cooking in grams. Canada officially metric since 1970 but many Canadians still use feet/inches for height and Fahrenheit for cooking. The lack of US adoption costs American businesses an estimated $1-2 billion annually in conversion-related errors and lost efficiency in international trade (NIST estimates).
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Note: Conversions use standard internationally recognized conversion factors. Temperature conversions use exact formulas. All values are calculated to high precision and displayed with up to 6 significant digits. US measurements are used for gallons, fluid ounces, cups, pints, and quarts.
Unit conversion is a fundamental skill used daily in cooking, travel, science, engineering, construction, and everyday life. The metric system (used by 95% of the world) and the imperial system (used primarily in the US, UK, and Liberia) require constant conversion for international communication. This converter handles 6 categories with over 40 unit types.
Length: 1 inch = 2.54 cm, 1 foot = 30.48 cm, 1 mile = 1.609 km. Weight: 1 pound = 0.454 kg, 1 ounce = 28.35 g. Volume: 1 gallon = 3.785 liters, 1 cup = 236.6 ml. Temperature: °F = °C × 1.8 + 32, water freezes at 0°C/32°F, boils at 100°C/212°F, body temperature is 37°C/98.6°F. Speed: 1 mph = 1.609 km/h, 60 mph ≈ 97 km/h, 100 km/h ≈ 62 mph.
For miles to km: multiply by 1.6 (or add 60%). For km to miles: multiply by 0.6. For Celsius to Fahrenheit: double and add 30 (approximate). For kg to lbs: double and add 10%. For liters to gallons: divide by 4. These approximations are accurate within 5% and useful when you need quick estimates without a calculator.