About the Unit Converter
The world measures in two main systems. Most countries use the metric system — metres, kilograms, litres and degrees Celsius — while the United States, and Britain in everyday life, still use imperial and US customary units such as inches, pounds, gallons and degrees Fahrenheit. Recipes, product labels, maps, weather forecasts, travel and school science all regularly need a quick, reliable way to move between the two.
This unit converter handles seven kinds of measurement in one place: length, weight, volume, area, temperature, speed and time. Choose the quantity, enter a value and pick the units to convert from and to. Alongside the answer it shows the exact conversion factor and the value in every other unit of the same kind, so one conversion answers several questions at once.
How to Use the Unit Converter
Choose what you want to convert: length, weight, volume, area, temperature, speed or time.
Enter the value.
Choose the unit to convert from and the unit to convert to. The unit lists change to match the quantity you picked.
The result appears with the factor used and the value in every unit of that kind.
How the Conversions Work
For every quantity except temperature, each unit has a fixed size in a base unit — the metre, kilogram, litre, square metre, metre per second or second. Converting is then a single multiplication and division:
result = value × (size of from-unit ÷ size of to-unit)
1 mile = 1,609.344 m and 1 km = 1,000 m
so 1 mile = 1,609.344 ÷ 1,000 = 1.609344 kmTemperature is different, because the Celsius and Fahrenheit scales have different zero points. The calculator converts through kelvin, which starts at absolute zero:
°C = (°F − 32) × 5/9 °F = °C × 9/5 + 32
K = °C + 273.15 °R = °F + 459.67Step-by-Step Example
Length: 1 mile to kilometres.
1 × 1.609344 = 1.60934 kmThe same mile is also 5,280 feet, 1,760 yards, 63,360 inches and about 0.868976 nautical miles.
Temperature: 100 °F to Celsius.
(100 − 32) × 5/9 = 68 × 5/9 = 37.7778 °CA normal body temperature of 37 °C is 98.6 °F.
Speed: 60 mph to km/h.
60 × 1.609344 = 96.5606 km/h60 mph is also about 26.8224 metres per second, 52.1386 knots and exactly 88 feet per second.
Why the Factors Are Exact
Until the middle of the twentieth century, the inch, pound and gallon were defined slightly differently in different countries. In 1959 the United States, Britain, Canada, Australia, New Zealand and South Africa agreed to define the inch as exactly 2.54 centimetres and the pound as exactly 0.45359237 kilograms. Every other imperial length and weight follows from those, so conversions between the systems can be done exactly, not approximately.
Volumes are the one area where the US and UK still differ. The US gallon is 231 cubic inches, exactly 3.785411784 litres, while the UK imperial gallon is exactly 4.54609 litres. Pints, quarts and fluid ounces differ too, so the converter lists US and UK versions separately.
Choosing the Right Unit
Some units have close cousins that are easy to confuse:
tonne (1,000 kg) vs US ton (907.185 kg) vs UK ton (1,016.05 kg)
nautical mile (1,852 m) vs statute mile (1,609.344 m)
US pint (473.176 ml) vs UK pint (568.261 ml)
knot (1 nautical mile per hour) vs mphWhen a number comes from a source in another country, check which version it uses before converting.
Rounding and Precision
The converter shows results to six significant figures, and exact values without unnecessary decimals. Six figures is more precise than almost any everyday measurement. For practical use, round to the precision of your original measurement: a room measured to the nearest centimetre does not need its area in square feet to four decimal places.
Time and Speed Units
Time units are the same everywhere, but they do not step by tens: 60 seconds make a minute, 60 minutes an hour, 24 hours a day and 7 days a week. For years, the converter uses the average Julian year of 365.25 days, which allows for leap years and is the standard in astronomy. So 1 hour is 3,600 seconds, 1 week is 168 hours, and 1 year is 8,766 hours or 31,557,600 seconds. For calendar work with specific dates, where months and leap years matter, a date calculator is a better tool.
Speed units combine a length and a time. Kilometres per hour divided by 3.6 gives metres per second, the unit used in physics, so 36 km/h is exactly 10 m/s. A knot is one nautical mile an hour, about 1.15078 mph, and is used at sea and in aviation.
Metric Prefixes
The metric system builds every unit from a base with the same prefixes, which is what makes metric conversions so simple. Kilo means a thousand, centi a hundredth, milli a thousandth and micro a millionth. A kilometre is 1,000 metres, a milligram a thousandth of a gram, and a millilitre a thousandth of a litre — moving between them is only a matter of shifting the decimal point.
Understanding Your Result
The headline is the converted value in the unit you chose.
The conversion factor shows how many of the target unit make one of the starting unit, or the formula for temperatures.
The in every unit line lists the value in all the other units of that quantity.
The worth knowing note explains how that kind of conversion is done.
When Should You Use This Calculator?
Use it when following recipes, instructions or plans written in another system.
Use it for travel — road signs, speed limits, fuel and weather abroad.
Use it for schoolwork and science, where SI units are standard.
Use it when shopping online from other countries, to understand sizes and quantities.
Common Mistakes
Mixing US and UK volumes. Gallons, pints and fluid ounces differ by up to 20 percent.
Using a length factor for an area. Square units need the factor squared.
Converting temperature differences with the formula. A rise of 10 °C is a rise of 18 °F, not 50 °F; only the scale, not the offset, applies to differences.
Rounding too early. Convert first, then round the final answer.
Confusing tonnes and tons. A metric tonne is 1,000 kg; US and UK tons are not.