Convert between units of length, weight, and temperature instantly. Supports metric, imperial, and more. Free online converter. This tool runs entirely in your browser — no data is sent to any server. It's fast, free, and works on any device.
Unit conversion touches daily life more than most people realize — cooking recipes from different countries, understanding foreign weather reports, calculating dosages, comparing international product specifications, and solving physics problems. This comprehensive converter handles length, weight/mass, volume, temperature, area, speed, time, data size, and more. It includes both metric and imperial units with precise conversion factors. Common conversions: 1 inch = 2.54 cm, 1 kg = 2.205 lbs, 1 gallon = 3.785 liters, °F = °C × 9/5 + 32. All conversions use exact mathematical factors — no rounding until the final display.
The US gallon (3.785 L) and Imperial gallon (4.546 L) diverged in 1824 when the UK redefined its gallon. The US kept the older Queen Anne wine gallon. This means US pints, quarts, and fluid ounces also differ from Imperial versions.
°C to °F: multiply by 9/5, add 32. °F to °C: subtract 32, multiply by 5/9. Kelvin = °C + 273.15. Key points: 0°C = 32°F (freezing), 100°C = 212°F (boiling), -40° is the same in both scales.
Mass (kg) is the amount of matter — constant everywhere. Weight (N) is the force of gravity on that mass — varies by location. On Earth's surface, the distinction is negligible for everyday purposes. In space, you have mass but essentially no weight.
The metric system was designed during the French Revolution to be logical and universal. Base 10 aligns with our decimal number system: kilo (1000), centi (1/100), milli (1/1000). Imperial units evolved organically from body parts (foot) and arbitrary standards (acre = area one ox can plow in a day).
Many are: 1 inch = exactly 2.54 cm, 1 pound = exactly 0.45359237 kg. Some are defined values, not measurements. Temperature conversions and some older units may involve rounding in practice, but the mathematical relationships are precise.