Applying a formula

To accurately calculate medicine dosage, a simple formula is used: what you want over what you've got times what it's in. This can be used for most applications. Applying a formula to calculate the exact amount required is particularly useful when calculating liquid medicines (elixirs or suspensions) or the amount of injection required.


Claire, a four year old child, weighs 18kg. She is prescribed a dose of 180mg Paracetamol in response to the formulary suggestion of 10mg to 15mg per kg. The formula can be used to calculate exactly the amount of medicine Claire requires.

The next pages show how to work out the dosage you need.

Creative Commons Licence
SMILE Calculating dosage by Gill Langmack and Caroline Burton, University of Nottingham modified by Marion Kelt, Glasgow Caledonian University is licensed under a Creative Commons Attribution 4.0 International LicenseBased on a work at