Drug calculations — the basics
What are drug calculations?
Drug calculations are about working out the right amount of a medicine. Here is an explanation, the topics involved and how to learn them.
Short definition
Drug calculations are about working out the right amount of a medicine from a prescription.
It might be how many tablets to give, how many mL to draw up, how much to dilute or what rate an infusion should run at. The aim is patient safety: a miscalculated dose can cause harm.
What topics are involved?
The content varies between courses, but these areas are common.
Measures and weights
Converting between g, mg and micrograms. Read more
Dosage calculations
Tablets, oral liquids and injections. Read more
Percentages and concentration
Dilution
Drops and infusions
Drops and infusion rates
Weight, body surface area and time
All the formulas are collected in the formulas page.
See also the complete guide to drug calculations.
How is it assessed?
This differs.
How the test is set up and what standards apply is decided by your university, employer or NHS trust and your course. Follow your course and local policy.
Frequently asked questions
What are drug calculations?+
Working out the right amount of a medicine from a prescription, for example the number of tablets, mL or the infusion rate.
Why are drug calculations important?+
A mistake in the calculation can lead to the wrong dose reaching the patient, which is why it is a central part of nursing education.
What topics are included?+
Commonly units, dosage calculations, percentages, dilution, drops, infusion rates and dose by weight or body surface area. It varies between universities.
How do you learn drug calculations?+
By working through lots of questions yourself, with a calculator and your steps written down.
Start practising in Dos
Now that you know what it is about, practise with tests of ten questions, a built-in calculator next to each question and statistics per topic.
