Convert length, weight, temperature, volume, area and speed between Metric, US Customary, UK Imperial and nautical units — built to work no matter which system your country uses.
Enter a length value to convert between units
Enter a weight value to convert between units
Enter a temperature to convert between scales
Enter a volume value to convert between units
Enter an area value to convert between units
Enter a speed value to convert between units
This free online unit converter and conversion calculator converts values between length, weight, temperature, volume, area, and speed units, covering Metric, US Customary, UK Imperial, and nautical systems in one tool. Acting as a universal unit converter and a metric to imperial converter for virtually any everyday measurement, it works as a dedicated length converter, weight converter, mass converter, temperature converter, volume converter, area converter, and speed converter all in one place — a true metric imperial converter for all countries rather than six separate tools. It's built for anyone who regularly deals with mixed measurement systems — travelers, students, cooks following recipes from another country, engineers, or shoppers comparing product specs listed in unfamiliar units.
Each tab (length, weight, temperature, volume, area, speed) lets you enter a value, pick a "from" unit, and instantly see it converted into every other unit in that category — whether that's km to miles, kg to pounds, liters to gallons, meters to feet, inches to cm, stone to pounds, or knots to mph. Most conversions use fixed multiplication factors relative to a base unit (for example, meters for length or kilograms for weight as a mass converter would use); the temperature converter instead uses the linear formulas °F = (°C × 9/5) + 32 and °C = (°F − 32) × 5/9 for a Celsius to Fahrenheit conversion, since Celsius and Fahrenheit scales don't share a zero point.
Unit mismatches cause real problems — comparing a US gallon vs UK gallon shows they differ by about 20%, a US ton and a metric tonne differ by roughly 10%, and confusing them in a recipe, shipping quote, or engineering spec can lead to meaningful errors. Having accurate, side-by-side conversions across systems — from a simple km to miles lookup to a full stone to pounds or knots to mph conversion — removes the guesswork and reduces costly mistakes when working across borders or unit conventions.
Almost every country uses the metric system (meters, kilograms, liters, Celsius) officially. The US primarily uses feet, pounds, gallons and Fahrenheit, while the UK commonly mixes both. This calculator groups units by system so you always know which you're using.
Celsius is used worldwide for weather and science, Fahrenheit is standard in the US, and Kelvin is the scientific base unit starting at absolute zero (−273.15°C). All three convert instantly and warn you if a result would fall below absolute zero.
A US gallon (3.785 L) and a UK/Imperial gallon (4.546 L) are about 20% different — the same applies to pints and fluid ounces. This calculator lists US Customary and UK/Imperial volume units in separate groups to prevent costly mix-ups in recipes and fuel economy figures.
Nautical miles and knots are the international standard for maritime and air navigation, based on the Earth's geometry rather than a national standard — making them consistent regardless of which country is operating the vessel or aircraft.
Common questions about unit conversion across measurement systems
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