Calculate bacterial or cell doubling time from OD600 or cell count data. Two-point and time-series modes with automatic exponential phase detection.
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Optical density measures light scattering, which correlates with cell density only within a limited range (typically OD 0.1–1.0). Above OD 1.0, the relationship becomes non-linear. Always calibrate OD600 against direct counts for your specific organism and spectrophotometer.
A smaller inoculum extends the lag phase but should not change the specific growth rate during log phase. If you observe different µ values with different inocula, check for density-dependent effects or quorum sensing.
Growth rate is highly temperature-dependent (Arrhenius relationship). A 10°C change can double or halve the growth rate. Always report the growth temperature alongside doubling time.
Two-point calculations are sensitive to measurement error. When possible, use the time-series mode with multiple readings during exponential growth to get a regression-based estimate with an confidence metric.
Two-point mode: direct application of Td = ln(2) / µ, where µ = ln(/N₁) / (t₂–t₁). Time-series mode: OLS linear regression on ln(value) vs. time with sliding-window exponential phase detection (minimum 3-point window, > 0.98 threshold). Growth rate and doubling time are derived from the regression slope.
Last validated 2026-04-05. Calculations are designed for planning and documentation support; verify procurement decisions against manufacturer specifications or institutional SOPs.
ConductScience Doubling Time Calculator (v1.0). ConductScience, Inc. 2026. Available at: https://conductscience.com/tools/doubling-time-calculator
Monod J. The growth of bacterial cultures. Annu Rev Microbiol. 1949;3:371–394.
Zwietering MH, et al. Modeling of the bacterial growth curve. Appl Environ Microbiol. 1990;56(6):1875–1881.
Microbial growth in batch culture follows the exponential model during the log phase:
Where: • N(t) = Population at time t (cells, OD600, CFU, etc.) • N₀ = Initial population • µ = Specific growth rate (h⁻¹) • t = Time
The doubling time is derived by setting N(t) = 2N₀:
This relationship holds only during balanced, unrestricted exponential growth. During lag or stationary phases, the model does not apply.
A typical microbial growth curve has four distinct phases:
• Lag phase: Cells adapt to new conditions — metabolic activity without division. Duration depends on inoculum age, media shift, and stress. • Exponential (log) phase: Constant µ, population doubles at regular intervals. This is the ONLY phase where Td is valid. • Stationary phase: Growth rate equals death rate. Nutrient depletion, waste accumulation, or quorum sensing limit growth. • Death (decline) phase: Viability decreases as nutrients are exhausted.
Common pitfall: measuring doubling time across phases (e.g., from lag into log) underestimates the true exponential growth rate. Always restrict your measurement to the log phase.
