Unit Conversion Formula Chart: Factors and Offsets

Build the chart around a stated direction

A useful formula chart names the original unit and the requested unit rather than listing a factor without direction. For length, centimetres = inches × 2.54, metres = feet × 0.3048, and kilometres = miles × 1.609344. For ordinary mass, kilograms = pounds × 0.45359237 and grams = ounces × 28.349523125. The pound and ounce entries use avoirdupois mass. To reverse one of these multiplicative conversions, divide by its listed factor instead of multiplying again.

Add volume entries with the convention written out

For volume, litres = cubic metres × 1,000 and millilitres = litres × 1,000. Litres = US liquid gallons × 3.785411784, while litres = Imperial gallons × 4.54609. Those gallon formulas belong on separate lines because the same generic label could otherwise hide the difference. A chart that includes cups or tablespoons should likewise specify its convention. The local Unit Converter uses US customary liquid volume options; the Imperial-gallon relationship above is an explicit formula rather than another available selector.

Give temperature its own formula column

For Celsius to Fahrenheit, F = 1.8C + 32. For Fahrenheit to Celsius, C = (F − 32)/1.8. Kelvin = Celsius + 273.15. These formulas have offsets, so their reverse direction is not found by merely dividing the original reading by a factor. For temperature differences, use ΔF = 1.8ΔC and ΔK = ΔC without the offsets. Keeping readings and differences on separate rows avoids applying a correct formula to the wrong type of quantity.

Verify a row before relying on the chart

Test a length row with 10 inches: multiplying by 2.54 gives 25.4 cm and dividing by 2.54 returns 10 inches. Test a temperature row with 0°C: the Fahrenheit formula gives 32°F, and the reverse returns zero. These two tests exercise different mathematical structures. If a chart is copied into a spreadsheet, retain the parentheses in the Fahrenheit numerator and label the input cells with their units. Do not extend a listed linear factor to an area, volume or unrelated physical quantity without deriving the required relationship.

Use dimensional cancellation to choose the factor direction

A conversion factor is a ratio of equal quantities, so its value is one even when its numerator and denominator have different unit names. Arrange the ratio so the unwanted unit cancels. For example, 3 m × 100 cm/1 m = 300 cm. Dividing by the same factor reverses the conversion. Write the unit symbols along with the numbers while setting up a chain; they show whether the expression ends in the requested unit. A numerically tidy result does not compensate for an uncancelled or inappropriate unit.

Apply powers to the whole conversion factor

If a length is squared to make an area, its conversion factor must also be squared. Since 1 m = 100 cm, 1 m² = 10,000 cm². For volume, cube the factor: 1 m³ = 1,000,000 cm³. Converting each dimension before multiplying gives the same result and is a useful independent check. Do not multiply a square-metre value by 100 merely because 100 is familiar from metres to centimetres. The exponent describes the physical dimension and changes the numerical conversion.

Recognize conversions that need another physical input

Mass and volume are different quantities, so kilograms cannot be converted into litres without density. Energy and temperature likewise need a heat-capacity model rather than a unit factor. Temperature readings are also special because Celsius and Fahrenheit require an offset, not only a multiplication. A general unit converter should be used within a compatible quantity family. If the requested pair crosses families, identify the missing physical relationship instead of trying several selector combinations until a numerical answer appears.

Keep SI prefixes case-sensitive

Milli denotes one thousandth, while kilo denotes one thousand. Thus 1,500 millimetres is 1.5 metres and 1.5 kilometres is 1,500 metres. In unit symbols, uppercase and lowercase can carry different meanings; MW means megawatt, while mW means milliwatt. Preserve the original capitalization when copying a chart into a form or spreadsheet.

Related guides

Grams to Ounces: Formula and Mass Examples

Divide grams by 28.349523125 for ordinary ounces, distinguish fluid and troy ounces, and convert a mixed pound-and-ounce mass without early rounding.

Pounds to Kilograms: Exact and Quick Methods

Multiply pounds by 0.45359237 for kilograms, compare the divide-by-2.2 estimate, and combine pounds with ounces before applying the conversion.

Kilograms to Pounds: Formula and Rounding

Convert kilograms to pounds with the exact pound definition, express a decimal result as pounds and ounces, and check a mixed-unit measurement.