Convert length, weight, temperature, volume, speed, and more — instantly.
Select a category (Length, Weight, Temperature, etc.) using the buttons at the top. Choose your source and target units, enter a value, and the result appears instantly. Hit the swap button (⇄) to reverse the conversion.
Cooking and recipe conversions: Recipe conversions are one of the most common unit conversion needs in everyday life. Key conversions to know: 1 cup = 240 ml, 1 tablespoon = 15 ml, 1 teaspoon = 5 ml, 1 fluid ounce = 30 ml, 1 pound (lb) = 454 grams. When scaling recipes, note that most volume measurements convert linearly, but baking (which is chemistry) may require adjusting leavening agents, salt, and cooking time disproportionately when doubling or halving.
Unit conversion in science and engineering: Scientific work almost exclusively uses SI units, but real-world engineering often requires bridging metric and imperial systems, particularly in the US. The 1999 Mars Climate Orbiter crash — a $327 million loss — was caused by a software unit mismatch where one team used pound-force seconds and another used newton seconds. Careful unit tracking and verification is fundamental to safe engineering practice.
Unit conversion is one of the most frequently needed everyday calculations — whether you are following a recipe in metric when you only know imperial measurements, checking how far a road trip will be in miles versus kilometres, or comparing product weights across different countries' labelling standards. Understanding the logic behind unit systems helps you convert confidently even without a calculator.
The metric system (SI): The International System of Units (SI) is used by most of the world and is the foundation of science and engineering globally. It is a decimal system — all units are related by powers of 10 — making conversions simple multiplications or divisions. The base units are the metre (length), kilogram (mass), second (time), kelvin (temperature), ampere (current), mole (substance), and candela (luminosity). Prefixes like kilo- (×1,000), centi- (÷100), and milli- (÷1,000) apply consistently across all units.
The imperial/US customary system: The United States (and to some extent the United Kingdom) still uses legacy units for everyday measurements: inches, feet, yards, and miles for length; ounces, pounds, and tons for weight; cups, pints, quarts, and gallons for volume. These units have no consistent decimal relationship, making conversions less intuitive. Note that UK and US imperial units differ: a US gallon is 3.785 litres while a UK (imperial) gallon is 4.546 litres, and fluid ounces also differ slightly.
Temperature conversion: Temperature is the most commonly misunderstood conversion because it uses an offset, not just a scale factor. To convert Celsius to Fahrenheit: multiply by 9/5 and add 32. To reverse, subtract 32 and multiply by 5/9. Some useful anchor points: 0°C = 32°F (water freezes), 100°C = 212°F (water boils), 37°C = 98.6°F (normal body temperature), and −40°C = −40°F (the only temperature where both scales are equal). Kelvin, used in science, starts at absolute zero: K = °C + 273.15.
Common conversions to memorise: A few key conversion factors are worth knowing by heart: 1 mile ≈ 1.609 km; 1 kg ≈ 2.205 lbs; 1 inch = 2.54 cm; 1 litre ≈ 0.264 US gallons; 1 foot = 30.48 cm. For quick mental conversions, rough approximations work well: multiply km by 0.6 to get miles, multiply kg by 2.2 to get lbs, and divide cm by 2.5 to get rough inches.