Generation time calculator.
Find a bacterial generation time. Enter the starting and ending cell numbers and the time between them, and the calculator returns the generation time and number of generations.
Counts and time
LiveThe number of generations is log base 2 of the fold increase. Generation time is the elapsed time divided by the number of generations.
Generation time
48.2 min
per generation
Assumes steady exponential (log-phase) growth. For lab estimates. Calculations run in your browser; nothing you enter is stored.
How it works
Time per generation
Generation time is how long a bacterial population takes to double, the same idea as doubling time but the usual term in microbiology. The number of generations between two counts is the log base 2 of the fold increase, and the generation time is the elapsed time divided by that number.
Growing from 1,000 to 1,000,000 cells is a thousand-fold rise, which is about 10 generations. Over 8 hours that is a generation time of roughly 48 minutes.
Reference
Generation time and rate.
How a generation time translates into doublings per hour during log-phase growth.
| Generation time | Doublings per hour |
|---|---|
| 20 min | 3.0 / h |
| 30 min | 2.0 / h |
| 60 min | 1.0 / h |
| 90 min | 0.7 / h |
| 120 min | 0.5 / h |
The full guide
The complete guide to generation time.
What generation time is, how to measure it, and what affects how fast bacteria grow.
What is generation time?
Generation time, or doubling time, is the interval a bacterial culture needs to double in number during exponential growth. It is a core measure in microbiology, used to compare strains, conditions and media. Fast growers like E. coli can double in about 20 minutes in rich media.
It is only meaningful during the log phase, when growth is exponential and unconstrained.
How to measure it
Take two cell counts a known time apart during log phase. The number of generations is the log base 2 of the final over the initial count, and the generation time is the time divided by that number of generations.
Using optical density readings works too, as long as you stay in the range where density tracks cell number.
What affects growth rate
Temperature, nutrients, oxygen and pH all change how fast bacteria grow. Each species has an optimum; away from it, generation time lengthens. Rich media and ideal temperature give the shortest generation times.
Stress, antibiotics or competition slow growth and stretch the generation time, which is often exactly what an experiment is measuring.
Generation time versus doubling time
The two terms are interchangeable: both mean the time to double. Microbiology favours generation time, often in minutes, while cell culture tends to say doubling time in hours. The maths is identical.
This calculator reports the answer in minutes to suit bacterial work; divide by 60 for hours.
The formula
One split
at a time.
Generations are log2 of the fold increase. Generation time is the elapsed time over the generations.
Doubling time ›# Generation time
n = log2(final / initial)
g = time / n
# worked example
8 h / log2(1000) = 48.2 minQuestions
Generation questions.
How do I calculate generation time?
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Find the number of generations as log base 2 of the final over the initial count, then divide the elapsed time by it. From 1,000 to 1,000,000 in 8 hours is about 48 minutes per generation.
What is the difference from doubling time?
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None in the maths; both are the time to double. Microbiology calls it generation time, often in minutes, while cell biology says doubling time in hours.
How many generations is a 1,000-fold increase?
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About 10, since two to the power of about 10 is roughly 1,000. More precisely it is log base 2 of 1,000, which is 9.97 generations.
What is a typical bacterial generation time?
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It varies widely. Fast growers like E. coli double in about 20 minutes in rich media at optimal temperature; many environmental bacteria are far slower.
Is this generation time calculator free?
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Yes. It is completely free with no sign-up, and every calculation runs locally in your browser, so nothing you enter is stored or sent anywhere.
About the developer
Jean Borg
Jean builds and maintains every calculator on freecalculators.pro from Malta, with a focus on tools that are fast, free and show their working. The generation time calculator uses standard log-phase growth maths and is for lab estimates.