Language, notation and formulas
Language, notation and formulas

This free course is available to start right now. Review the full course description and key learning outcomes and create an account and enrol if you want a free statement of participation.

Free course

Language, notation and formulas

3.4 Converting units by using a formula

It is sometimes necessary to convert from one unit of measurement to another. You can use a formula in order to do this.

Example 11

Use the formula 1 pint = 0.5683 litres (to 4 s.f.) to calculate the number of litres in 8 pints (or 1 gallon). Give your answer to 3 significant figures.


As 1 pint is 0.5683 litre, it follows that 8 pints will be 8 times this:

  8 pints = 8 × (0.5683 litre) = 4.55 litres (to 3 s.f.).

Sometimes the conversion formula that is given is in the opposite direction from the one you want. However, it is possible to turn such formulas round. For example, since 1 km = 1000 m, it follows that

Example 12

Turn the formula 1 mile = 1.609 km round to obtain 1 km in miles. Give your answer to 3 significant figures.


The formula can be written as

Dividing by 1.609 gives


For further information, take a look at our frequently asked questions which may give you the support you need.

Have a question?
Free Courses

OpenLearn has over 800 free courses across all our subjects designed by our academic experts. From 1 to 100 hours, introductory to advanced, you can start learning at any time and all for free.