How It Works
This calculator works in 4 steps.
Enter the custom factor
Type any factor greater than 1, such as 3 or 3.162.
Enter starting concentration and tube count
Type C₀ and the number of tubes.
Set the volume kept per tube
Type the diluent volume per tube, such as 200 µL.
Read the series
The calculator returns concentrations, transfer volume V_d / (F − 1), and the actual factor after volume rounding.
The Formula
The formula divides the starting concentration by the custom factor raised to the step number.
Cₙ = C₀ / FⁿV_t = V_d / (F − 1)p = 1 / log₁₀(F)- F:
- Custom factor per step
- C₀:
- Starting concentration
- V_d:
- Diluent volume per tube
- V_t:
- Transfer volume
- p:
- Points per tenfold range
A factor of 3 from 100 µM gives 100, 33.3, 11.1, 3.70, and 1.23 µM. With 200 µL diluent per tube, transfer 100 µL at each step.
Conversion Table
The conversion table shows 5-step series from 100 µM and the transfer volume per 200 µL diluent for 6 factors.
| Factor | Series (µM) | Transfer volume | Diluent per tube |
|---|---|---|---|
| 1.5 | 100 → 66.7 → 44.4 → 29.6 → 19.8 | 400 µL | 200 µL |
| 2 | 100 → 50 → 25 → 12.5 → 6.25 | 200 µL | 200 µL |
| 3 | 100 → 33.3 → 11.1 → 3.7 → 1.23 | 100 µL | 200 µL |
| 3.162 | 100 → 31.6 → 10 → 3.16 → 1 | 92.51 µL | 200 µL |
| 4 | 100 → 25 → 6.25 → 1.56 → 0.391 | 66.67 µL | 200 µL |
| 5 | 100 → 20 → 4 → 0.8 → 0.16 | 50 µL | 200 µL |
What Is the Custom-Factor Serial Dilution Calculator?
The Custom-Factor Serial Dilution Calculator is a serial dilution tool that applies one user-chosen factor, including non-integer values such as 1.5, 3, or √10 (3.162), at every step. The factor stays constant, so the concentrations form a geometric series.
Non-standard factors give finer spacing than twofold or tenfold series. A half-log series (factor 3.162) places 2 points per decade, and a factor of 1.5 places 5.7 points per decade. The calculator returns transfer volumes rounded to pipette-friendly values and recalculates the exact factor after rounding.
Common Uses
There are 5 main uses of this calculator.
Half-log dose curves
Pharmacologists use factor 3.162 for even spacing on a log axis.
IC₅₀ and EC₅₀ studies
Researchers use threefold steps to cover 3 to 4 decades with 8 to 10 points.
Enzyme kinetics
Biochemists space substrate concentrations around the Michaelis constant (Km).
Sensitivity testing
Labs use 1.5-fold steps for narrow-range detection limits.
Assay optimization
Developers test reagent concentrations with a factor matched to the expected range.