How to Convert Between Metric & Imperial Measurements

Written by michael mcgrath
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How to Convert Between Metric & Imperial Measurements
Imperial and metric conversion requires set formulas. (steel ruler image by dwags from

The imperial system of measurement originated in Britain. Imperial measurements include inches, pounds and pints. The metric system was developed in France and uses meters, kilograms and litres. Most countries now use the metric system, while America continues to use imperial measurements. A simple set of formulas allows you to convert between the two measurement systems. Memorising the numbers for each conversion takes time, so it's helpful to use conversion sheets or an online converter.

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  1. 1

    Convert from inches to millimetres by multiplying millimetres by 25.4. Convert inches to centimetres by multiply inches by 2.54. Converting feet to meters requires multiplying by 3.281, and to convert miles to kilometres multiply by 1.609.

  2. 2

    Multiply by 0.0394 to convert millimetres to inches. To convert centimetres to inches, multiply the centimetres by 0.3937. To convert meters to feet multiply by 3.281, and kilometres to miles requires multiplying the number of kilometres by 0.6214.

  3. 3

    Convert imperial ounces to metric grams by multiplying by 28.35. Convert pounds to grams by multiplying by 453.6. To convert pounds to kilograms, multiply by 0.4536, and to convert tons to kilograms multiply by 1016.05.

  4. 4

    Multiply by 0.03527 to convert from metric grams to imperial ounces. If you want to convert grams to pounds, multiply by 0.002205. Convert kilograms to pounds by multiplying kilograms by 2.205, and to convert kilograms to tons multiply by 0.0009842.

  5. 5

    Multiply by 0.0296 to convert a US fluid ounce to a metric litre. Convert US pints to litres by multiplying by 0.4731 and convert US gallons to litres by multiplying by 3.785. US imperial liquid measurements differ slightly from older British imperial measurements.

  6. 6

    Convert metric litres to US imperial pints by multiplying litres by 2.114. Convert litres to US gallons by multiplying the amount of litres by 0.2642.

Tips and warnings

  • The numbers required to convert from imperial to metric and back again are difficult to remember. If you need to perform conversion calculations regularly, keep a list of conversion numbers handy.
  • Errors in conversion can have serious repercussions. Use online conversion calculators for quick and accurate conversion between the two measurement systems.

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