Bacterial growth calculator
Growth rate, doubling time and time to a target OD from two OD600 readings.
Growth rate, doubling time and time to a target OD from two OD600 readings.
In log phase a culture grows exponentially, so the optical density at 600 nm rises as OD(t) = OD₀ · eμt. Two readings taken during that phase are enough to solve for thespecific growth rate μ:
μ has units of h⁻¹ (or min⁻¹). It depends on the strain, the medium, temperature and aeration, so measure it under the conditions you actually use rather than assuming a textbook value.
The doubling time, also called generation time, is how long the population takes to double. It follows directly from μ:
The number of generations between the two readings is log₂(OD₂ / OD₁). For OD 0.1 → 0.4 that is 2 generations, so μ = ln(4) / 2 h = 0.693 h⁻¹ and the doubling time is 1.0 h. If you already know the doubling time and want to go the other way, use thedoubling time calculator.
The most common use is timing the harvest: competent cells at OD 0.4–0.6, IPTG induction at OD 0.6–0.8, or a flask that must hit OD 1.0 before the next step. Extrapolating the same exponential curve gives
The result is reported as elapsed time and as minutes after the second reading, so you can set a timer. The prediction assumes growth stays exponential; the closer the target is to the second reading, the more reliable it is.
| Organism and conditions | Doubling time |
|---|---|
| E. coli, LB, 37 °C, shaking | 20–30 min |
| E. coli, M9 minimal glucose, 37 °C | 45–60 min |
| E. coli, LB, 30 °C | 40–60 min |
| Bacillus subtilis, LB, 37 °C | 25–40 min |
| Saccharomyces cerevisiae, YPD, 30 °C | 90–120 min |
| Mycobacterium tuberculosis | 18–24 h |
Take two OD600 readings in log phase. The specific growth rate is μ = ln(OD2 / OD1) / (t2 − t1), and the doubling time is ln(2) / μ. OD 0.1 to 0.4 over 2 hours gives μ = 0.693 h⁻¹ and a doubling time of 1.0 hour.
Assuming exponential growth continues, the time to the target is t = t2 + ln(OD_target / OD2) / μ, where μ is the growth rate from the two readings. For OD 0.4 at 2 h with μ = 0.693 h⁻¹, OD 0.6 is reached at 2.58 h, about 35 minutes after the second reading.
Only exponential (log-phase) growth, roughly OD600 0.1 to 0.8 for E. coli in rich medium. Below 0.05 readings are noisy, and above about 1 the spectrophotometer response is no longer linear and growth slows, so predictions drift.
About 20 minutes in LB at 37 °C with good aeration, 30 to 40 minutes in minimal medium, and longer at lower temperatures or in expression strains carrying a burdensome plasmid.
Yes. Generation time is the interval in which the population doubles. The number of generations between two readings is log2(OD2 / OD1).