Nursing Dosage Calculator guide
Nursing Dosage Calculator: Drug Calculations Made Simple
Use our nursing dosage calculator to practise and check drug calculations: liquid volumes, tablets, mg/kg doses, infusion rates and drip rates.
By the AllCalculator editorial teamUpdated 15 October 20262 min read
Drug calculations are a core skill for nurses, midwives and student nurses, and a common part of numeracy assessments. Our Nursing Dosage Calculator covers the standard formulas so you can practise and check your working.
Important: this calculator is for learning and checking only. Always follow the prescription, local policies and a second independent check before giving any medicine.
How to use the calculator (Nursing Dosage Calculator)
- Choose the type of calculation.
- Enter the values from the prescription and the medicine you have.
The formulas
Liquids and injections
Volume = what you want ÷ what you've got × what it's in
For 250mg prescribed, with a stock of 500mg in 5mL: 250 ÷ 500 × 5 = 2.5mL.
Tablets
Tablets = dose prescribed ÷ strength of one tablet
For 1g prescribed and 500mg tablets, convert to the same units first: 1,000 ÷ 500 = 2 tablets.
Weight-based doses
Dose = mg per kg × weight in kg
For 15mg/kg and a 20kg child: 300mg per dose. Always check against the maximum dose in the BNF or BNFc.
Infusion rate
mL per hour = volume ÷ time in hours
1,000mL over 8 hours is 125mL/hour.
Drip rate
Drops per minute = volume × drop factor ÷ time in minutes
1,000mL over 8 hours with a 20 drops/mL set: 1,000 × 20 ÷ 480 = 42 drops/minute.
Tips for avoiding errors
- Convert units first: 1g = 1,000mg and 1mg = 1,000 micrograms.
- Estimate first: if the answer looks odd, like 14 tablets, stop and check.
- Write micrograms in full, not mcg or µg, to avoid misreading.
For converting units, see our Unit Converter.
Frequently asked questions
What's the "what you want, what you've got" formula?
It's another name for D ÷ H × V: the dose desired, divided by the dose you have, times the volume it's in.
What drop factor should I use?
Standard giving sets are usually 20 drops/mL, blood sets 15 drops/mL and paediatric burettes 60 drops/mL. Check the packaging.
Can I use this at work?
Only as a check alongside your own calculation and local procedures, never instead of them.
Practise with the Nursing Dosage Calculator to build confidence for your numeracy assessments.
Sources and further reading
- NMC: The Codenmc.org.uk
- BNF: British National Formularybnf.nice.org.uk
- Royal Pharmaceutical Society: Safe and secure handling of medicinesrpharms.com
Links open official and independent websites in a new tab.
This guide is general information to help you understand your options. It isn't financial, tax, legal or building advice and doesn't take your personal circumstances into account. Figures were checked when the guide was last updated and can change, so confirm anything important with GOV.UK, HMRC, a regulated adviser or a qualified tradesperson.