How It Works
This calculator works in 4 steps.
Enter stock and final concentrations
Type C₀ and C_final in the same unit.
Enter final volume and minimum transfer
Type the working volume and the smallest volume the pipette handles well, such as 1 µL or 2 µL.
Split the total factor
The calculator divides the total DF into a stage-1 factor and a stage-2 factor, starting near the square root.
Read both stages
The result lists the intermediate concentration, the stage-1 volumes, and the stage-2 volumes.
The Formula
The formula splits the total dilution factor into 2 stage factors whose product equals the total.
DF_total = C₀ / C_finalDF_total = DF₁ × DF₂C_int = C₀ / DF₁V_int = V_final / DF₂- C₀:
- Stock concentration
- C_int:
- Intermediate concentration
- C_final:
- Working concentration
- DF₁ / DF₂:
- Stage factors
A 10 mM (10,000 µM) stock to 1 µM in 1 mL is a 1:10,000 dilution, which needs 0.1 µL direct. A 1:100 predilution gives a 100 µM intermediate, and 10 µL of it in 1 mL gives 1 µM.
Conversion Table
The conversion table compares direct transfer volume with a 2-stage plan for 5 high-factor dilutions.
| Dilution | Total DF | Direct transfer | Stage 1 | Stage 2 | Stage-2 transfer |
|---|---|---|---|---|---|
| 10 mM → 1 µM | 10,000 | 0.1 µL | 1:100 (100 µM) | 1:100 | 10 µL |
| 1 mM → 10 nM | 100,000 | 0.01 µL | 1:1,000 (1 µM) | 1:100 | 10 µL |
| 100 µM → 50 nM | 2,000 | 0.5 µL | 1:20 (5 µM) | 1:100 | 10 µL |
| 5 mM → 0.5 µM | 10,000 | 0.1 µL | 1:50 (100 µM) | 1:200 | 5 µL |
| 1 mg/mL → 20 ng/mL | 50,000 | 0.02 µL | 1:500 (2 µg/mL) | 1:100 | 10 µL |
What Is the Intermediate Stock Calculator?
The Intermediate Stock Calculator is a planning tool that inserts a predilution stage between a concentrated stock and the final working solution, so every transfer stays at a measurable volume. The tool splits one large dilution factor into 2 smaller factors whose product equals the original factor.
Direct dilutions above 1:1,000 often call for sub-microliter transfers. Pipette error rises sharply below 1 µL, so a 0.1 µL transfer carries far more relative error than a 10 µL transfer. The calculator returns the intermediate concentration, the volumes for each stage, and the volume of intermediate left over.
Common Uses
There are 5 main uses of this calculator.
Compound dosing
Cell biologists predilute 10 mM DMSO stocks before adding nM doses to medium.
Cytokine and growth factor dosing
Researchers dilute µg/mL stocks to pg/mL working levels in 2 stages.
Primer and probe dilution
Molecular labs make 10 µM intermediates from 100 µM stocks.
Trace element standards
Analysts dilute 1,000 mg/L standards to µg/L levels through an intermediate.
Solvent control
Users lower the carried-over DMSO percentage by adding the predilution step.