How It Works
This calculator works in 4 steps.
Enter the culture density
Type OD600 (corrected for any reading dilution) or cells/mL.
Enter the target density
Type the target OD600, cells/mL, or a ratio such as 1:100.
Enter the final volume
Type the volume of fresh culture.
Read the volumes
The calculator returns culture and medium volumes.
The Formula
The formula applies C₁V₁ = C₂V₂ with OD600 as the density measure.
V₁ = OD_target × V₂ / OD_cultureOD_culture = OD_read × DF_readcells/mL = OD × k (species-specific)- OD_culture:
- Culture OD600
- OD_target:
- Target OD600
- DF_read:
- Dilution used for the reading
- k:
- User-supplied cells per mL per OD unit
An overnight culture reads 0.24 after a 1:10 dilution, so OD600 = 2.4. For 50 mL at OD 0.05, add 1.04 mL culture to 48.96 mL medium.
Conversion Table
The conversion table gives culture volumes for 6 OD600 back-dilutions.
| Culture OD600 | Target OD600 | Final volume | Culture volume | DF |
|---|---|---|---|---|
| 2.4 | 0.05 | 50 mL | 1.042 mL (1,042 µL) | 48 |
| 1.8 | 0.1 | 25 mL | 1.389 mL (1,389 µL) | 18 |
| 3 | 0.02 | 100 mL | 0.6667 mL (666.7 µL) | 150 |
| 0.9 | 0.05 | 10 mL | 0.5556 mL (555.6 µL) | 18 |
| 4.5 | 0.01 | 200 mL | 0.4444 mL (444.4 µL) | 450 |
| 1.2 | 0.2 | 5 mL | 0.8333 mL (833.3 µL) | 6 |
What Is the Bacterial Culture Dilution Calculator?
The Bacterial Culture Dilution Calculator is a tool that applies a specified dilution to a bacterial culture, by optical density at 600 nm (OD600), cells/mL, or ratio, and returns the culture and medium volumes. The calculator treats OD600 as proportional to cell density within the linear range of the spectrophotometer.
Back-dilution of an overnight culture to OD600 0.05 or 0.1 restarts growth at a known density. OD600 readings above about 1.0 leave the linear range on many instruments, so the calculator asks for a diluted reading and multiplies by the reading dilution. The OD-to-cell conversion depends on species and instrument, so the user supplies it.
Common Uses
There are 5 main uses of this calculator.
Growth curves
Microbiologists start cultures at a common OD600.
Protein expression
Users dilute overnight cultures 1:100 for induction runs.
Competent cell prep
Labs grow cultures from a set start OD to mid-log.
Inoculum preparation
Labs prepare standardized inocula for susceptibility tests.
Phage infection
Virologists set host cell density before infection.