Doubling Time Calculator
⏱️ Doubling Time Results
Doubling Time (Generation Time)
—
Specific Growth Rate (µ)
—
per hour
Elapsed Time
—
between measurements
Generations in Period
—
number of doublings
Fold Increase
—
N₂ / N₁
How to Use the Doubling Time Calculator
Enter two OD600 readings (or cell counts) measured at two different time points during exponential growth. Both measurements must be taken during the log phase for accurate results.
- N₁ and N₂: OD600 readings or CFU/mL values at two time points.
- Time 1 and Time 2: The clock times when each measurement was taken (in minutes or hours).
- Log phase only: Measurements must be in the exponential growth phase. Lag or stationary phase data will give inaccurate results.
Doubling Time Formula
µ = (ln N₂ − ln N₁) / (t₂ − t₁)
td = ln(2) / µ = 0.693 / µ
Where:
µ = specific growth rate (hr⁻¹)
td = doubling time (generation time)
N₁, N₂ = OD600 or cell count at t₁, t₂
Example:
OD₁ = 0.2 at t₁ = 0 hr, OD₂ = 0.8 at t₂ = 2 hr
µ = (ln 0.8 − ln 0.2) / 2 = 0.693 hr⁻¹
td = 0.693 / 0.693 = 1.0 hour
td = ln(2) / µ = 0.693 / µ
Where:
µ = specific growth rate (hr⁻¹)
td = doubling time (generation time)
N₁, N₂ = OD600 or cell count at t₁, t₂
Example:
OD₁ = 0.2 at t₁ = 0 hr, OD₂ = 0.8 at t₂ = 2 hr
µ = (ln 0.8 − ln 0.2) / 2 = 0.693 hr⁻¹
td = 0.693 / 0.693 = 1.0 hour
Typical Doubling Times by Organism
- E. coli (37°C, LB): ~20 minutes — fastest commonly used lab strain
- Bacillus subtilis: ~25–30 minutes
- Staphylococcus aureus: ~30–60 minutes
- Saccharomyces cerevisiae: ~90 minutes at 30°C
- Mycobacterium tuberculosis: ~18–24 hours
- Caulobacter crescentus: ~90–120 minutes