Generation Time Calculator

Generation time is the time it takes a microbial population to complete one generation, doubling in number through binary fission. It is calculated from an initial population count, a final population count, and the elapsed incubation time, and is the standard way to quantify how fast bacteria, yeast, or other microbes are growing.

First find the number of generations n = log2(Nt/N0), then generation time g = t / n. For example, a culture growing from 1,000 to 1,024,000 CFU/mL (a 1024-fold increase, exactly 2 to the 10th power) over 200 minutes has n = 10 generations, so g = 200 / 10 = 20 minutes per generation, the classic E. coli optimal generation time.

For a simple population where every cell divides in two, generation time and doubling time describe the same underlying process and are numerically identical. Generation time is the term typically used in microbiology and fermentation, and is usually reported alongside the number of generations elapsed, doubling time is more common in general cell biology and cancer research, see the Cell Doubling Time Calculator for that framing.

Number of generations n = log2(Nt/N0), the base-2 logarithm of the fold-increase in population. For example, a population that grows from 2x10^6 to 6.4x10^7 CFU/mL has increased 32-fold, and log2(32) = 5, meaning exactly 5 generations occurred.

Specific growth rate, mu, is the exponential growth rate constant, expressed per unit time (commonly per minute or per hour). It relates to generation time by mu = ln(2) / g, a higher mu means faster growth and a shorter generation time. Fermentation and bioprocess engineers use mu as the standard metric for comparing growth conditions.

It varies enormously by species and conditions. Escherichia coli in rich broth at 37 degrees C can have a generation time as short as about 20 minutes. Many environmental and slow-growing bacteria (e.g. some soil or marine species) can take many hours or even days per generation, generation time is highly specific to the organism and growth conditions.

No. This calculation assumes the culture is in exponential (log) phase growth for the entire measured interval. If your counts span the lag phase (before growth starts) or stationary phase (after growth slows or stops), the calculated generation time will not accurately represent the culture's true log-phase growth rate.

Generation time and specific growth rate are used to predict how quickly a starter culture will reach a target cell density, to schedule feeding and harvest times in a bioreactor, and to compare how different media, temperature, or aeration conditions affect microbial productivity.

This calculator's examples use minutes, a common unit for fast-growing bacteria, but any consistent time unit works, the generation time result and specific growth rate will be reported in whatever time unit you entered for the elapsed incubation time.

Generation time describes a growth rate, and a rate cannot be determined from a single measurement. You need an initial count (N0), a final count (Nt) after a known elapsed incubation time (t), to calculate how many generations occurred and how long each one took.

Yes, the underlying math (binary or budding division doubling a population each generation) applies to yeast and other unicellular eukaryotes just as it does to bacteria, only the typical generation time values differ, yeast generation times are often reported in hours rather than the minutes typical of fast-growing bacteria.