Dilution CFU Calculator
Enter colony count, dilution factor, and plated volume to calculate the CFU/mL of your original sample.
Single Plate Calculation
Calculate CFU/mL from one plate count.
10 ^
Enter a negative integer, e.g. -3 means 10⁻³ = 0.001
Spread plate = 0.1 mL | Pour plate = 1 mL
Multi-Plate Average
Average 2–4 plates from different dilutions (30–300 colony rule).
Single Plate Result
CFU / mL
CFU / L
Formula used
Multi-Plate Average Result
Average CFU / mL
Average CFU / L
| Colonies | Dilution | Volume (mL) | CFU/mL | Valid? |
|---|
Fill in the fields on the left and click Calculate.
Serial Dilution Reference
| Dilution steps (1:10 each) | Dilution factor | Decimal |
|---|---|---|
| 1 | 10⁻¹ | 0.1 |
| 2 | 10⁻² | 0.01 |
| 3 | 10⁻³ | 0.001 |
| 4 | 10⁻⁴ | 0.0001 |
| 5 | 10⁻⁵ | 0.00001 |
| 6 | 10⁻⁶ | 0.000001 |
Summary
Enter colony count, dilution factor, and plated volume to calculate the CFU/mL of your original sample.
How it works
- Enter the number of colonies counted on your agar plate.
- Enter the dilution factor used (e.g. 0.001 for a 10⁻³ dilution, or enter the exponent directly).
- Enter the volume plated in mL (typically 0.1 mL for spread plates or 1 mL for pour plates).
- The calculator applies the formula: CFU/mL = colonies ÷ (dilution factor × volume plated).
- Results are shown in CFU/mL and CFU/L, with scientific notation for large values.
Use cases
- Determine bacterial load in a broth culture after serial dilution plating.
- Quantify microbial contamination in food or water samples.
- Calculate viable cell counts for inoculation in fermentation experiments.
- Verify starter culture concentrations in dairy or beverage production.
- Monitor growth curves by tracking CFU/mL over time during batch culture.
- Assess antibiotic efficacy by comparing pre- and post-treatment plate counts.
Frequently Asked Questions
Last updated: 2026-07-01 ·
Reviewed by Nham Vu