Reconstitution Mathematics Guide
Reconstitution maths answers one question: how much liquid should be added to a known amount of powder to get a chosen concentration? This guide covers the arithmetic only and is not medical advice.
What the calculation means
Dissolving powder in liquid does not change how much powder there is. It only sets how concentrated the solution is. More liquid means a lower concentration; less liquid means a higher one.
The inputs
- The total amount in the vial (mg or mcg).
- Either the volume of liquid you add (mL) or the concentration you want (mg/mL).
The formulas
Concentration = amount ÷ volume.
Volume = amount ÷ concentration.
Worked example (mathematical example only)
A 5 mg vial at a chosen 2.5 mg/mL needs 5 ÷ 2.5 = 2 mL. Check it backwards: 5 mg ÷ 2 mL = 2.5 mg/mL. A 10 mg vial at 5 mg/mL also needs 10 ÷ 5 = 2 mL.
An assumption to know about
The calculator assumes the final volume equals the volume of liquid you enter. It does not add the small volume taken up by the powder itself.
Common mistakes
- Entering the vial amount in mcg while reading the answer as mg.
- Dividing concentration by amount instead of amount by concentration.
- Rounding too early. Keep full numbers until the last step.
Related calculators
Reconstitution calculator · Concentration calculator · Concentration guide
Mathematical calculation only. Not medical advice.