How It Works
This calculator works in 4 steps.
Enter the target concentration (C₂)
Type the concentration required in the finished solution or assay well.
Enter the final volume (V₂)
Type the total volume of the finished solution.
Enter the fixed stock volume (V₁)
Type the volume of stock to be added, such as 1 µL per 1 mL of medium.
Read the required stock concentration
The calculator multiplies C₂ by V₂, divides by V₁, and shows C₁ with the × strength label.
The Formula
The formula multiplies the target concentration by the ratio of final volume to stock volume.
C₁ = C₂ × (V₂ / V₁)× strength = V₂ / V₁- C₁:
- Required stock concentration
- C₂:
- Target concentration
- V₁:
- Fixed stock volume
- V₂:
- Final volume
A cell assay needs 10 µM drug in 1 mL of medium with 1 µL of stock added. C₁ = 10 µM × 1000 µL / 1 µL = 10,000 µM (10 mM), a 1000× stock.
Conversion Table
The conversion table shows the required stock concentration for 6 target concentrations and fixed transfer volumes.
| Target (C₂) | Final volume (V₂) | Stock volume (V₁) | Required stock (C₁) | Stock strength |
|---|---|---|---|---|
| 1 mM | 100 mL | 10 mL | 10 mM | 10× |
| 0.5 M | 50 mL | 1 mL | 25 M | 50× |
| 10 µg/mL | 1,000 mL | 2 mL | 5,000 µg/mL | 500× |
| 2 mg/mL | 25 mL | 0.5 mL | 100 mg/mL | 50× |
| 0.1 µM | 10 mL | 0.1 mL | 10 µM | 100× |
| 5 % | 200 mL | 50 mL | 20 % | 4× |
What Is the Initial Concentration Calculator?
The Initial Concentration Calculator is a dilution tool that returns the stock concentration (C₁) required for a fixed stock volume to reach a target concentration in a fixed final volume. The tool works backward from the bench constraint, such as "I can only add 10 µL", to the stock strength that makes that transfer correct.
Initial concentration planning applies when a stock is made in-house, such as a 1000× drug stock in dimethyl sulfoxide (DMSO). The calculator returns C₁ in the same unit as C₂ and reports the stock-to-final multiplier, for example 1000×.
Common Uses
There are 5 main uses of this calculator.
1000× compound stocks
Cell biologists make DMSO stocks that keep the final solvent at 0.1% (1 µL per mL).
Fixed-volume additions
Assay developers set a stock strength that suits a 2 µL robotic addition.
Stock solution planning
Technicians decide how concentrated a stock must be before weighing the solid.
Solvent limit compliance
Researchers keep carrier solvent below a protocol limit by raising the stock strength.
Reagent kit design
Kit makers set component concentrations as 5×, 10×, or 50× for simple user mixing.