Reconstitution Calculator

Quickly determine the diluent volume, final concentration, or drug mass needed for reconstituting powdered medications. Select what you want to calculate and enter the known values.

Mass of dry powdered drug in milligrams

Volume of liquid diluent to add in milliliters

Target concentration after reconstitution

Total volume after reconstitution

Reconstitution Formula: C = m / V Where: • C = Final concentration (mg/mL) • m = Mass of powdered drug (mg) • V = Total final volume after reconstitution (mL) Solving for Different Variables: 1. Diluent Volume: V = m / C Diluent = V - Powder Volume Displacement 2. Final Concentration: C = m / V 3. Drug Mass Required: m = C × V Powder Volume Displacement: Most powders displace approximately 5% of the final volume. Always consult manufacturer specifications for exact reconstitution instructions.
Example 1: Finding Diluent Volume You have: 500 mg vial of antibiotic powder Need: 100 mg/mL solution Volume = 500 / 100 = 5.0 mL total Diluent needed ≈ 4.75 mL (accounting for ~0.25 mL powder displacement) Example 2: Finding Final Concentration You have: 1000 mg vial of vancomycin You add: 10 mL of sterile water Final concentration = 1000 / 10 = 100 mg/mL Each 1 mL of solution contains 100 mg of drug Example 3: Finding Drug Mass Needed Need: 50 mg/mL solution Target final volume: 4 mL Drug mass required = 50 × 4 = 200 mg Example 4: Pediatric Dose Preparation Prescribed: 150 mg of a 250 mg/vial drug Add 5 mL diluent → 250/5 = 50 mg/mL Volume to administer = 150/50 = 3.0 mL Common Diluents: • Sterile Water for Injection (SWFI) • Bacteriostatic Water (0.9% benzyl alcohol) • 0.9% Sodium Chloride (normal saline) • 5% Dextrose in Water (D5W)

What is drug reconstitution?

Reconstitution is the process of adding a liquid diluent (such as sterile water, saline, or bacteriostatic water) to a powdered medication to create a solution for injection or infusion. Many medications are stored as lyophilized (freeze-dried) powders to maintain stability, and must be reconstituted immediately before use.

How do I calculate the volume of diluent needed?

The volume of diluent needed depends on the desired final concentration. Using the formula C = m/V, where C is concentration, m is drug mass, and V is volume: V = m/C. For example, if you have 500 mg of powder and want a 100 mg/mL solution, you need V = 500/100 = 5 mL of diluent (accounting for the powder volume displacement).

Why does the powder displace some volume?

The powdered drug occupies a certain volume that adds to the total when diluent is added. This is called powder volume displacement or powder volume. For most medications, the powder volume is small (0.1-0.5 mL), but for some drugs it can be significant. Always check the manufacturer instructions for the exact final volume.

How should reconstituted medications be stored?

Storage depends on the specific medication. Most reconstituted drugs must be refrigerated at 2-8°C and used within a specific timeframe (often 24 hours to 30 days). Some can be stored at room temperature. Always follow manufacturer guidelines. Never freeze reconstituted medications unless explicitly stated, and never use a solution that appears cloudy or contains particles.

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