How It Works
This calculator works in 4 steps.
Enter the starting concentration
Type the stock value, such as 2 × 10⁹ CFU/mL.
Set the number of tubes
Choose 1 to 12 decimal steps.
Set the tube volume
Choose 1 mL into 9 mL, 100 µL into 900 µL, or a custom transfer.
Read each dilution
The calculator lists 10⁻¹ to 10⁻ⁿ with expected concentration and expected colonies per plated volume.
The Formula
The formula divides the starting concentration by 10 raised to the tube number.
Cₙ = C₀ × 10⁻ⁿV_t : V_d = 1 : 9Colonies = Cₙ × V_plated- Cₙ:
- Concentration in tube n
- C₀:
- Starting concentration
- n:
- Number of tenfold steps
- V_plated:
- Volume spread on a plate
A culture at 2 × 10⁹ CFU/mL diluted to 10⁻⁷ holds 200 CFU/mL. Plating 0.1 mL (100 µL) gives about 20 colonies.
Conversion Table
The conversion table shows a 9-tube decimal series from 2 × 10⁹ CFU/mL with expected colonies per 0.1 mL plated.
| Dilution | Cumulative DF | Concentration | Colonies per 0.1 mL |
|---|---|---|---|
| Neat (10⁰) | 1 | 2 × 10⁹ CFU/mL | 2 × 10⁸ |
| 10⁻¹ | 10 | 2 × 10⁸ CFU/mL | 2 × 10⁷ |
| 10⁻² | 100 | 2 × 10⁷ CFU/mL | 2 × 10⁶ |
| 10⁻³ | 1,000 | 2 × 10⁶ CFU/mL | 2 × 10⁵ |
| 10⁻⁴ | 10,000 | 2 × 10⁵ CFU/mL | 2 × 10⁴ |
| 10⁻⁵ | 100,000 | 2 × 10⁴ CFU/mL | 2 × 10³ |
| 10⁻⁶ | 1,000,000 | 2 × 10³ CFU/mL | 200 |
| 10⁻⁷ | 10,000,000 | 2 × 10² CFU/mL | 20 |
| 10⁻⁸ | 100,000,000 | 2 × 10¹ CFU/mL | 2 |
What Is the Tenfold Serial Dilution Calculator?
The Tenfold Serial Dilution Calculator is a tool that reduces the concentration by a factor of 10 at each step and returns the concentration, dilution exponent, and volumes for each tube. A standard tenfold step transfers 1 part into 9 parts diluent, such as 100 µL into 900 µL or 1 mL into 9 mL.
Tenfold series (decimal or log dilutions) span large ranges with few tubes. Eight tenfold steps cover 8 orders of magnitude, from 10⁹ down to 10¹ cells per mL. Microbiology plate counts, viral plaque assays, and qPCR standard curves use this series.
Common Uses
There are 5 main uses of this calculator.
Bacterial plate counts
Microbiologists find the dilution that gives 30 to 300 colonies per plate.
Viral plaque assays
Virologists dilute virus stocks to count 10 to 100 plaques per well.
qPCR standard curves
Molecular labs make 5 to 7 log steps of a DNA standard.
Disinfectant efficacy tests
Labs measure log reductions by plating tenfold series before and after treatment.
Food and water testing
Food labs follow ISO 6887 decimal dilution steps for sample enumeration.