Nursing dose calculator
Six calculations from the French nursing curriculum, each broken down step by step. The point is not to hand you a number: it is to show the reasoning so you can reproduce it on your own.
Educational tool for practice only. It applies the values you enter and never suggests a dosage. In a care setting it replaces neither the prescription, the package insert, ward protocols, nor independent double-checking by a second professional.
How to calculate the volume to draw up
The method never changes, whatever the prescription: harmonise the units, then divide the prescribed dose by the available concentration.
1. Harmonise the units
The prescribed dose and the amount printed on the label must use the same unit. 1 g = 1,000 mg, 1 mg = 1,000 µg. Confusing µg and mg is a thousand-fold error.
2. Work out the concentration
Concentration is the amount of active ingredient divided by the reference volume printed on the ampoule or vial. A 1 g vial in 10 mL gives 100 mg/mL.
3. Apply the formula
Volume to draw up = prescribed dose ÷ available concentration. For 500 mg prescribed at 100 mg/mL, you draw up 5 mL.
4. Check backwards
Multiply the volume you found by the concentration: you must land back on the prescribed dose. This reflex catches most calculation errors.
The method sheets
Each calculation in this tool maps to a detailed sheet with worked examples.
Frequently asked questions
How do you convert grams to milligrams?
Multiply by 1,000: 1.5 g = 1,500 mg. Every step down the unit hierarchy (g → mg → µg → ng) multiplies by 1,000; every step up divides by 1,000.
How do you calculate an infusion rate in drops per minute?
Rate (drops/min) = volume in mL × 20 ÷ duration in minutes, for an adult macrodrop set. Equivalent shortcut: the rate in mL/h divided by 3. A paediatric microdrop set delivers 60 drops per mL.
What is the dilution formula?
C1 × V1 = C2 × V2, since the amount of active ingredient is identical before and after dilution. From it you get the volume of stock solution to draw up, then the solvent to add as the difference to the final volume.
How do you calculate a paediatric dose by weight?
Dose = posology in mg/kg × actual weight in kg, always using a same-day weighing. The resulting dose must then be checked against the therapeutic range and any maximum set by protocol.
Can this calculator be used on placement?
No. It is a practice tool built for assessments and personal study. In a care setting the prescription, the package insert, ward protocols and independent double-checking by a second professional remain the only reference.