Free Unit Converter Online

A recipe says 350°F. Your oven shows Celsius. A bookshelf is listed as 30 inches and you need to know if it fits a 75 cm gap. The flight is 800 km, the rental car shows mph. Real life keeps mixing measurement systems and our free online Unit Converter is the calmest possible way to handle that. Type a number, pick what unit it is now, pick what unit you want, and the answer appears instantly — no ads in the middle, no app to install, no signup. The tool covers seven full categories: length (millimetres to miles, including nautical and astronomical units), weight and mass (milligrams to metric tons, ounces, pounds, stones), temperature (Celsius, Fahrenheit, Kelvin, Rankine), volume (millilitres, litres, cups, pints, quarts, gallons in both US and Imperial varieties), speed (metres per second, kilometres per hour, miles per hour, knots), area (square metres, hectares, acres, square miles), and data storage (bits and bytes through petabytes, with proper handling of the binary 1024-based prefixes versus decimal 1000-based prefixes that confuses everyone). Conversions run locally with double-precision floating-point arithmetic, which means the result is accurate to about 15 significant digits — far more than any practical use needs. Common scenarios this tool covers: converting cooking temperatures and quantities between US recipes and metric kitchens; checking that an imported electronics product's rated wattage and voltage make sense for your local mains; comparing fuel efficiency between mpg and L/100km when reading car reviews from different countries; verifying flight distances and speeds; sizing furniture in inches against a metric floor plan; understanding cloud storage pricing where providers casually mix GB and GiB; and homework or exam prep where you need a fast cross-check on a manual calculation. The temperature converter handles the offsets correctly — Celsius and Fahrenheit are not a simple ratio because they have different zero points, and Kelvin starts at absolute zero — which is the kind of thing that catches careless converters out and quietly produces wrong answers. If you are working with currency rather than physical units, the [Currency Converter](/tools/currency-converter) handles real-time exchange rates separately. For time zones, the [Timezone Converter](/tools/timezone-converter) is a better fit. And if you need to convert numbers themselves — written words to digits or vice versa — the [Number to Words](/tools/number-to-words) tool is purpose-built for that. Everything here works on phone, tablet, and desktop, and there is no usage limit because there is no server cost — the maths happens entirely in your browser the moment you type.