How this unit converter works
This online unit conversion tool uses standard conversion factors between a single “base” unit in each category. For most categories (length, area, volume, weight, time, digital storage, energy, frequency, pressure, speed and fuel economy) each unit is represented as a fixed factor relative to a base unit (for example, meters for length or joules for energy). The calculator:
- converts your input value from the selected “from” unit to the base unit;
- translates the base-unit value into the chosen “to” unit; and
- rounds the result to a readable number of decimal places.
Temperature and fuel economy are handled slightly differently because they are not simple one-step linear conversions. For temperature, the unit converter first converts to Celsius, then to Kelvin or Fahrenheit using the correct offset and scale. For fuel economy, the calculator uses kilometres per litre (km/L) as a reference and applies the inverse relationship for litres per 100 kilometres (L/100km), as well as the correct conversions for US mpg and imperial mpg.
Supported unit types in this converter
- Length: meters, kilometres, centimetres, millimetres, micrometres, nanometres, miles, yards, feet, inches, light years.
- Temperature: Celsius, Fahrenheit, Kelvin.
- Area: square meters, kilometres, centimetres, millimetres, micrometres, hectares, acres and more.
- Volume: cubic meters, litres, millilitres, US and imperial gallons, quarts, pints, cups, fluid ounces, tablespoons, teaspoons, and cubic units.
- Weight / Mass: kilograms, grams, milligrams, metric tons, long tons, short tons, pounds, ounces, carats, atomic mass units.
- Time: seconds, milliseconds, microseconds, nanoseconds, picoseconds, minutes, hours, days, weeks, months, years.
- Digital storage: bits, bytes, kilobytes, kibibytes, megabytes, mebibytes, gigabytes, gibibytes, terabytes, tebibytes and beyond.
- Energy: joules, kilojoules, calories, kilocalories, BTU, watt-hours, kilowatt-hours, electronvolts.
- Frequency: hertz, kilohertz, megahertz, gigahertz, terahertz.
- Fuel economy: miles per US gallon, miles per imperial gallon, kilometres per litre, litres per 100 km.
- Pressure: pascals, kilopascals, bar, millibar, psi, atmospheres, Torr.
- Speed: meters per second, kilometres per hour, miles per hour, knots, feet per second.
Popular metric to imperial conversions
- Length: convert meters to feet, centimetres to inches, or kilometres to miles for travel and construction.
- Temperature: quickly switch between Celsius and Fahrenheit for cooking, weather, or lab work.
- Volume: compare litres to US gallons or imperial gallons when looking at fuel tanks or packaging.
- Weight: convert kilograms to pounds or grams to ounces for shipping, recipes, or gym weights.
- Fuel economy: translate European L/100km ratings into North American mpg to compare cars.
- Digital storage: see how many GiB are in 1 TB when comparing hard drives and SSDs.
This metric and imperial unit converter is designed for everyday use: shopping, travel, DIY projects, school work and quick checks. All results are approximate and may involve rounding. For engineering, scientific, or regulatory purposes, always double-check with official standards, specifications, or professional tools.
Pounds and the metric system: a short history
Pounds: where this unit comes from
The word “pound” comes from the Latin libra, a Roman unit of weight that spread through medieval Europe. Over time, different kinds of pounds appeared in England and other countries, including the troy pound (used for precious metals) and the avoirdupois pound (used for everyday goods).
The modern pound in everyday use is the avoirdupois pound. It is divided into 16 ounces and contains exactly 7,000 grains. This version of the pound became standard for trade in Britain and later in many English-speaking countries.
In the late 19th and 20th centuries, countries moved to define traditional units using the metric system. In 1893 the United States defined the pound in terms of the kilogram, and in 1959 several English-speaking nations signed the International Yard and Pound Agreement, fixing the international pound at exactly 0.45359237 kilograms. This definition is still used today.
The metric system: how it started
Before the metric system, Europe used hundreds of local units. Even the same “pound” or “foot” could mean different values in different towns, which made trade and science difficult. During the French Revolution, reformers wanted a single, logical system of measures based on nature and simple decimal steps.
In 1799 France introduced the first practical metric system. The metre was defined from the Earth’s meridian, and the kilogram from the mass of a specific volume of water. Platinum standards for the metre and kilogram were made and used as official references for about 90 years.
The metric idea gradually spread. In 1875 many countries signed the Treaty of the Metre, creating international bodies to maintain common standards. In 1960 the modern International System of Units (SI) was launched, based on a small set of base units with decimal prefixes. Today almost all countries use the metric system as their main system of measurement, even where pounds and other traditional units are still familiar in everyday life.