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Unit Conversion Calculator
Choose what you are measuring, then the starting unit and the target unit. One tool covers thirteen categories, with exact factors and a list of the same quantity in the other units of that family.
How every conversion is done
All the units in a category are tied to one base unit: the metre for length, the kilogram for mass, the square metre for area, the litre for volume, metres per second for speed, the pascal for pressure, the joule for energy, the watt for power, the second for time, the byte for data and the degree for angles. A conversion has two steps. First the value is multiplied by the factor that converts the starting unit into the base unit; then it is divided by the factor of the target unit.
result = value × factor(from) ÷ factor(to)
Going through a base unit means that any pair works without a separate table for every combination. Temperature is the exception, because Celsius, Fahrenheit, Kelvin and Rankine differ by an offset as well as a scale, so it has its own formulas.
What each category covers
| Category | Units included |
|---|---|
| Length | micrometre to kilometre, inch, foot, yard, mile, nautical mile |
| Weight | milligram to tonne, ounce, pound, stone, tons, troy ounce, carat |
| Volume | mL, L, m³, US and imperial gallons, quarts, pints, ounces, cups |
| Pressure | Pa, kPa, MPa, bar, atm, psi, torr, mmHg |
| Energy and power | J, kWh, kcal, BTU, watts, kilowatts, horsepower |
| Time and data | milliseconds to decades, bits to petabytes in decimal and binary |
Each family also has its own page with background, a longer reference table and mistakes to avoid: see the length, weight and temperature converters, among others.
What the tool cannot convert
The calculator will not turn one kind of quantity into another. Kilograms cannot become litres without knowing the density of the substance, and miles per hour cannot become kilometres without also being a speed. For cooking, where volume and weight meet through density, use the cooking converter. For fuel economy, which is an inverse relationship, use the fuel economy converter.
Regional units such as the marla, kanal and tola have their own tools, because their definitions vary and must be confirmed by the user.
Avoiding common errors
- Check which gallon, ton or ounce. US and imperial versions of the same word differ by many percent.
- Do not round early. Chain conversions at full precision and round the last answer.
- Keep readings and differences apart. A temperature change of 5 °C is 9 °F, while a reading of 5 °C is 41 °F.
- Read prefixes. Milli, kilo and mega differ by factors of a thousand, and binary and decimal data prefixes differ by a few percent.
As a sanity check, estimate the answer in your head first. Kilometres should come out smaller than miles when converting from miles, and gigabytes should be larger than gibibytes for the same amount of data.
Worked example
You want to know how many kilometres are in a 5-mile run.
Inputs
| What are you converting? | Length |
|---|---|
| Value | 5 |
| From | Miles (mi) |
| To | Kilometres (km) |
Result
5 mi = 8.04672 km
| Micrometres (µm) | 8,046,720,000 |
|---|---|
| Millimetres (mm) | 8,046,720 |
| Centimetres (cm) | 804,672 |
| Metres (m) | 8,046.72 |
| Inches (in) | 316,800 |
| Feet (ft) | 26,400 |
| Yards (yd) | 8,800 |
| Nautical miles (nmi) | 4.344881 |
- Only units of the same kind can be converted. Choose the category first, then the two units.
Accuracy note: Factors use the standard definitions stated on this page. Results are rounded for display; for engineering or legal work use the full-precision factors.
Frequently asked questions
How do I convert between units?
Select the category, enter the value, and choose the starting and target units. The calculator multiplies by the starting unit's factor to reach the base unit, then divides by the target's factor.
Which categories are supported?
Length, weight, temperature, area, volume, speed, pressure, energy, power, time, data storage, angle and force, each with the common metric, US and imperial units.
Are the conversion factors exact?
Most are exact definitions, such as 1 inch = 25.4 mm and 1 pound = 0.45359237 kg. A few, like the Mach reference or the average year, are stated conventions explained on their own pages.
Why can I not convert kilograms to litres?
They measure different things, mass and volume. A conversion needs the density of the material, which differs for water, oil, flour and everything else.
Is my data stored anywhere?
No. The conversion runs in your browser and nothing you enter is sent or saved.
Related calculators
More conversion references
For more unit converters beyond this tool, see PakMath more unit converters. PakMath is a sister project of Adzita.