This converter is provided for general reference only. Conversion factors are standard international definitions. Always verify critical measurements with a certified instrument.
Unit converter
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Type a number in the field above and select a unit. All conversions update instantly.
Unit conversion using international standard definitions
This tool converts a value from one unit to another across five categories: length, weight, temperature, area and volume. The conversion factors used are standard international definitions, so a converted figure carries no error of its own. Any difference from an expected result comes from the input value or from rounding the output.
How this calculator works
The converter multiplies the value entered by a fixed conversion factor to the target unit, or for temperature applies a set formula. The imperial and US customary length and weight factors come from the 1959 International Yard and Pound Agreement, to which Australia was a signatory, and are exact by definition.
Worked example
Because the factors are exact, conversions are direct. A 12 inch length is 12 times 2.54, which is 30.48 centimetres. A 10 pound weight is 10 times 0.45359237, which is 4.5359237 kilograms. A temperature of 25 degrees Celsius is 25 times 9, divided by 5, plus 32, which is 77 degrees Fahrenheit.
The converter applies the standard factor to the value entered.
What changes your conversion result
The conversion factors below are defined constants, not approximations. The main ones are:
Length
The defining length factors are exact: 1 inch is 2.54 centimetres, 1 foot is 0.3048 metres, 1 yard is 0.9144 metres, and 1 mile is 1.609344 kilometres. Metric steps are also exact, with 1 metre being 100 centimetres or 1000 millimetres, and 1 kilometre being 1000 metres.
Weight
The defining mass factor is exact: 1 avoirdupois pound is 0.45359237 kilograms, which is 453.59237 grams. From this, 1 ounce is one sixteenth of a pound and 1 stone is 14 pounds. Metric steps are exact, with 1 kilogram being 1000 grams and 1 tonne being 1000 kilograms.
Temperature
Temperature uses formulas rather than a single factor. To convert Celsius to Fahrenheit, multiply by 9, divide by 5 and add 32. To convert Fahrenheit to Celsius, subtract 32, multiply by 5 and divide by 9. To convert Celsius to kelvin, add 273.15, since the kelvin is the SI base unit of temperature and 0 kelvin is absolute zero.
Area and volume
Area and volume units are derived from the length definitions above, so they are also exact. For area, 1 hectare is 10000 square metres and 1 acre is 4046.8564224 square metres. For volume, 1 litre is 1000 millilitres and 1 cubic metre is 1000 litres. The volume units in this converter use US customary definitions, which differ from imperial units of the same name, so a US gallon is not the same as an imperial gallon.
Input accuracy
The accuracy of the value entered is the main source of any difference between a converted result and an expected figure.
Decimal rounding
How many decimal places the result is rounded to can affect the displayed figure, especially for conversions with long decimal factors.
Unit selection
Whether the intended unit is selected matters, since some names such as ounce, pint and gallon exist in more than one system with different values.
US customary vs imperial volume
For volume in particular, whether the unit is US customary or imperial affects the result, as a US gallon, pint, cup and fluid ounce are each smaller than the imperial unit of the same name.
Rates and assumptions used
| Item | Value used | Source |
|---|---|---|
| Exact length, weight, area and volume conversion factors and the SI base units | Standard international definitions (exact by agreement) | NIST Special Publication 811, Guide for the Use of the International System of Units |
Figures checked against the sources above on 11 August 2026.
Frequently asked questions
Yes for the defined units. The inch, foot, yard, mile and pound are fixed exactly by the 1959 International Yard and Pound Agreement, so the conversion adds no error of its own. Any difference in a result comes from the input value or from rounding.
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Sources
Content reviewed and figures checked against the sources above on 11 August 2026.