Reconstitution Calculator
Powdered drugs are mixed with a diluent first. Enter the concentration the label gives after mixing and the ordered dose, or the vial amount and dose to count full doses.
Shows the work. Answer, formula, and numbered steps, rounded the way nursing exams expect. For study and exam practice, not for patient care.
Formula
mL = ordered dose ÷ concentration after mixing.
Fill in the fields and press Calculate to see the answer and every step.
For study and exam practice, not for patient care.
Rounding: Volumes of 1 mL or more round to the tenth; under 1 mL, to the hundredth. Full doses per vial round down.
Terms: Reconstitution, Diluent, Concentration
Worked examples
Cefazolin 0.5 g IM is ordered. The 1 g vial label says: add 10 mL of sterile water for a concentration of 100 mg/mL.
- Solve for
- Volume to give (mL)
- Vial amount
- 1 g
- Diluent added
- 10 mL
- Concentration after mixing
- 100 mg/mL
- Ordered dose
- 0.5 g
Formula mL = ordered dose ÷ concentration after mixing.
- Adding 10 mL to the 1 g vial gives 100 mg/mL (from the label).
- Convert the order to the label's unit: 0.5 g = 500 mg.
- mL = ordered dose ÷ concentration.
- 500 mg ÷ 100 mg/mL = 5 mL.
- 5 mL is exact, so no rounding is needed.
Answer 5 mL
Penicillin G 5 million units is ordered. How many full doses does a 20 million unit vial give?
- Solve for
- Full doses per vial
- Vial amount
- 20,000,000 units
- Dose
- 5,000,000 units
Formula mL = ordered dose ÷ concentration after mixing.
- Doses = vial amount ÷ dose = 20 million units ÷ 5 million units = 4.
- Only full doses count, so round down: 4 doses.
Answer 4 doses
FAQ
How do you calculate a reconstituted dose?
Use the concentration the label gives after mixing: mL = ordered dose ÷ concentration (per mL). Convert the order to the label's unit first.
Does the diluent volume equal the final volume?
Not always: the powder can add volume. Use the concentration printed on the label for the diluent you added, not the diluent volume alone.
How many doses are in a vial?
Divide the drug in the vial by the ordered dose and round down: only full doses count.