Compounding Concentration Calculator
Calculate dilution volumes using the C1V1 = C2V2 formula for pharmacy compounding and lab preparations.
About this calculator
Pharmacy compounding and laboratory dilution both rely on one conservation principle: the total amount of active ingredient does not change when you dilute it, only its concentration does. That principle is captured in the classic dilution equation C1V1 = C2V2, where C1 and V1 are the stock solution's concentration and the volume of it you use, and C2 and V2 are the desired final concentration and final volume. Rearranged to solve for the unknown, V1 = (C2 x V2) / C1 -- the volume of stock solution needed.
The remaining volume to reach the desired final volume is made up with diluent (water, saline, or another vehicle depending on the preparation), so volume of diluent = desired final volume minus volume of stock needed. This calculator also reports the dilution factor (stock concentration divided by desired concentration), which describes how many times more concentrated the stock is than the target -- a dilution factor of 10 means the stock is diluted 1-part-in-10 to reach the target concentration. The "available stock volume" input is recorded for reference only (to confirm you have enough stock on hand) and does not change the calculated volumes, since the calculation only needs the stock's CONCENTRATION, not how much of it you happen to have in the bottle.
Medical Disclaimer
This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about your health. Never disregard professional medical advice or delay seeking it because of results from this tool.
Inputs
Results
Volume of Stock Needed (V1)
10 mL
Volume of Diluent
90 mL
How to Use This Calculator
- Enter the Stock Concentration (C1) in mg/mL — the concentration of your starting solution.
- Enter the Available Stock Volume in mL (for reference; this does not affect the calculation).
- Enter the Desired Concentration (C2) in mg/mL — the target concentration of the final preparation.
- Enter the Desired Final Volume (V2) in mL — the total volume you need to prepare.
- Review the Volume of Stock Needed (V1 in mL) and Volume of Diluent to add — combine these two volumes to produce the final preparation at the target concentration.
How the result changes with Stock Concentration (C1)
| Stock Concentration (C1) | Volume of Stock Needed (V1) | Volume of Diluent |
|---|---|---|
| 50 | 20 mL | 80 mL |
| 75 | 13.33 mL | 86.67 mL |
| 150 | 6.67 mL | 93.33 mL |
| 250 | 4 mL | 96 mL |
What each input means
- Stock Concentration (C1)
- Concentration of the stock solution in mg/mL (or any consistent unit).
- Available Stock Volume
- Total volume of stock solution available (for reference only).
- Desired Concentration (C2)
- Target concentration of the final solution in mg/mL.
- Desired Final Volume (V2)
- Desired total volume of the final diluted solution in mL.
How this is calculated
Formula
C1 × V1 = C2 × V2 → V1 = (C2 × V2) / C1Worked example, using the default values
- Identify Input Parameters4 parametersStock Concentration (C1) = 100, Available Stock Volume = 500, Desired Concentration (C2) = 10, Desired Final Volume (V2) = 100 = 4 input(s) provided
- Calculate Volume of Stock NeededVolume of Stock Needed10 = 10
- Calculate Volume of DiluentVolume of Diluent90 = 90
- Calculate Dilution FactorDilution Factor10 = 10
Engine last updated . Checked against 1 independently-derived test — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does entering the available stock volume not change the calculated result?
The C1V1 = C2V2 equation only needs the stock solution's CONCENTRATION (C1), not the total volume you have on hand. The "available stock volume" field is provided purely as a reference check -- to confirm your bottle actually contains enough of the volume the calculation says you need -- and never enters the volume-of-stock or volume-of-diluent formulas.
How does raising the desired final volume change the amount of stock solution needed?
Volume of stock needed scales directly and proportionally with the desired final volume, since V1 = (C2 x V2) / C1: doubling the desired final volume while holding the stock and target concentrations fixed doubles the volume of stock solution required (and, correspondingly, the volume of diluent needed to reach that larger final volume).
What does the dilution factor actually describe?
The dilution factor is the stock concentration divided by the desired concentration, and it describes the ratio of the two -- a dilution factor of 20 means the target concentration is 1/20th as concentrated as the stock, so 1 part of stock combined with 19 parts of diluent (20 parts total) yields the target. It is a convenient way to express the same relationship the volume calculation already captures, without needing a specific final volume in mind.
Why does a more concentrated stock solution need less volume for the same final preparation?
Because V1 = (C2 x V2) / C1, volume of stock needed is inversely proportional to the stock concentration when the target concentration and final volume are held fixed -- doubling the stock concentration halves the volume of stock required to hit the same target. A more concentrated stock delivers the same total amount of active ingredient in a smaller volume, which is exactly what dilution accounts for.
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