Calculating drug dosage

Calculating drug dosage

Calculating correct medication dosages is an essential skill within all medical and related disciplines. Patients need accurate dosages of prescribed medicines to fulfil their treatment regimes. One problem is that children do not come in a standard size and so need only a part of a vial rather than all of it.

The importance of calculations

Before starting to measure out the medicine and preparing to give it, the medicine needs to be calculated precisely. 1ml syringes have graduations of 0.01 to 0.99, so medicines less than 1ml need to be calculated to two decimal places. 2.5ml, 5ml, and 10ml syringes have graduations of 0.1ml so need to be calculated to one decimal place.

Rounding decimals up and down

To be accurate, medicines need to be calculated to one decimal place beyond that required in order to round the value up (if the second decimal place is 5 or over) or down (if the second decimal place is less than 5).

In a 1ml syringe, the value required would need to be calculated to three decimal places in order to round up or down as appropriate.

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