Reconstitution calculator explained
When you add diluent to a lyophilized drug or concentrated reagent, you want a final solution with a specific strength. This calculator applies the relationship so that entering the dose amount {mass} and target volume {volume} returns the required reconstitution concentration {reconstitution}. It keeps the ratio transparent whether you work in mg/mL, units/mL, or g/L.
Use it in pharmacy clean rooms, biotech labs, or QC suites whenever you need to scale instructions or double-check calculations before compounding.
How the conversion works
Let be the amount of active ingredient in the vial, the desired final concentration, and the final volume. Then
If a vial contains multiple doses, calculate the concentration once and then draw individual dose volumes with . The calculator simplifies this by letting you enter any two quantities and solving for the third.
Units and conversions
| Quantity | Units | Notes |
|---|---|---|
| Mass | mg, units, or g | Match the labeling on the vial. |
| Final volume | mL | Total volume after diluent addition. |
| Concentration | mg/mL, units/mL | Output that defines how strong the solution is. |
Worked examples
- Antibiotic vial
Powder vial contains 1.0 g cefazolin. Desired concentration is 100 mg/mL for IV push.
Add sterile diluent to reach 10 mL total volume; each 2 mL withdraw provides a 200 mg dose.
- Laboratory enzyme stock
Need 5 mL of a 25 U/mL solution from a vial labeled 500 units total.
Use the calculator to confirm the reconstitution concentration, then take 0.25 mL to deliver 25 units.
Tips and pitfalls
- Mix gently after adding diluent to avoid foaming proteins or denaturing enzymes.
- Use bacteriostatic diluent only when labeling allows; some biologics require preservative-free diluent.
- Adjust for displacement volume if the powder significantly increases final volume (common with large biotech products).
- Label syringes and vials with both total concentration and per-dose draw volume to prevent medication errors.