Reconstitution Calculator — Drug Powder to Solution
Reconstituting a lyophilised (freeze-dried) medication means dissolving the powder in a measured volume of diluent to reach a target concentration. Enter the drug amount, diluent volume, and desired dose to find the resulting concentration and the volume you need to withdraw.
mg
mL
mg
Drug mass per millilitre after adding the diluent
- 1
Reconstituted concentration
500 mg ÷ 10 mL = 50 - 2
Volume to withdraw for desired dose
250 mg ÷ 50 mg/mL = 5
How does this calculator work?
Concentration (mg/mL) = drug amount ÷ diluent volume. Volume to withdraw = desired dose ÷ concentration. For a 500 mg vial + 10 mL diluent: 50 mg/mL; a 250 mg dose needs 5 mL. Always verify diluent type and volume against the product monograph.
Formula
How this is calculated
Many injectable medicines — antibiotics, biologics, lyophilised proteins — are stored as a dry powder because they are unstable in solution. Before administration, a specific volume of diluent (sterile water for injection, normal saline, or bacteriostatic water as directed by the package insert) is added to the vial. The drug dissolves and the total solution volume equals approximately the added diluent volume (powder displacement is usually negligible unless the package insert states otherwise).
The resulting concentration C = mass / volume (mg per mL). Once the concentration is known, the volume needed to deliver a prescribed dose is simply: volume = dose / concentration. For example: a 500 mg vial reconstituted with 10 mL yields 50 mg/mL; a 250 mg dose requires 5 mL.
Always follow the manufacturer's product monograph for the exact diluent type, volume, storage conditions, and beyond-use date of the reconstituted solution. This calculator assumes complete dissolution and no significant powder displacement. Units can be scaled (mcg/mcg/mL or g/g/mL) as long as drug amount and desired dose use the same unit.
Frequently asked questions
For most small-molecule drugs the displacement volume is negligible. For large-molecule biologics or when precision matters, check the package insert — it sometimes states the exact reconstituted volume or a displacement value to account for.
Yes. As long as drug amount and desired dose are both in the same unit (mg, mcg, g), the concentration and withdrawal volume remain consistent. The formula is purely a ratio.
Always follow the product monograph. Common diluents include sterile water for injection (SWFI), 0.9% sodium chloride (normal saline), or 5% dextrose. Using the wrong diluent can cause precipitation, degradation or patient harm.
Also known as
TG we-Calculate Editorial Team. (2026). Reconstitution Calculator — Drug Powder to Solution [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/reconstitution-calculator
TG we-Calculate Editorial Team. "Reconstitution Calculator — Drug Powder to Solution." TG we-Calculate. 2026. https://we-calculate.com/calculator/reconstitution-calculator.
TG we-Calculate Editorial Team, "Reconstitution Calculator — Drug Powder to Solution," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/reconstitution-calculator
@misc{wecalculate_reconstitution_calculator, title = {Reconstitution Calculator — Drug Powder to Solution}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/reconstitution-calculator}}, year = {2026}, note = {TG we-Calculate} }
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