Pharmacy tools
Dilution Calculator
Use C₁V₁ = C₂V₂ to find how much stock and diluent you need for a target concentration and volume.
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Version 1.0.0 · Last reviewed
Tool
Result
Live output from your inputs
Enter values and calculate to see results.
How it worksShow guideHide guide
Introduction
Solve C₁V₁ = C₂V₂ to find how much stock solution to measure when preparing a weaker dilution to a target volume. Use the same concentration and volume units throughout.
Disclaimer: This tool is for informational purposes only and is not professional medical, pharmaceutical, financial, or tax advice. Always verify doses with a licensed clinician or pharmacist.
Formula
Alligation via concentration-volume equality: stock volume needed is desired concentration times desired volume, divided by stock concentration. Diluent fills the remainder.
- C1 — Stock concentration
- V1 — Stock volume to take
- C2 — Desired concentration
- V2 — Desired final volume
Step-by-step
- Enter stock (starting) concentration.
- Enter the desired (final) concentration — must be lower than stock.
- Enter the desired final volume.
Worked example
To make 100 mL of 2% from 10% stock, take 20 mL stock and add 80 mL diluent.
Use cases
- Prepare a weaker solution from a concentrated stock
- Check compounding dilution math
- Teach pharmacy technician concentration problems
Frequently asked questions
Do units have to match?
Yes. Keep concentration units consistent (both % w/v, both mg/mL, etc.) and volume units consistent (both mL).
What about alligation alternate?
This tool covers simple dilution from one stock. Mixing two strengths to an intermediate is a separate alligation problem (coming soon).
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