Bacterial Growth Calculator
Estimate how many bacteria are present after a period of exponential division from the starting count, doubling time and elapsed time.
How it works
Generations = elapsed time ÷ doubling time · Final count = initial · 2^generations
Bacteria in the exponential (log) phase of growth divide by binary fission, doubling their number every generation. The number of generations is simply the elapsed time divided by the doubling (generation) time, and each generation multiplies the population by two. Because the growth is a power of two, counts climb extraordinarily fast — a single cell dividing every 20 minutes would exceed a billion in under 11 hours if resources allowed.
Worked example
From 1,000 cells with a 20-minute doubling time, 120 minutes gives 120 ÷ 20 = 6 generations. The final count is 1,000 × 2⁶ = 1,000 × 64 = 64,000 cells.
Sources: Bacterial growth — Wikipedia
Frequently asked questions
What is a doubling time?
The doubling or generation time is how long a population takes to double during exponential growth. For fast-growing bacteria like E. coli it can be around 20 minutes under ideal lab conditions, but it lengthens sharply as nutrients run low.
Does this growth continue forever?
No. Exponential doubling only holds during the log phase. As nutrients deplete and waste builds up, growth slows into the stationary phase and eventually declines — real cultures follow an S-shaped, then falling, curve.
Can the number of generations be a fraction?
Yes. If the elapsed time is not a whole multiple of the doubling time, the generation count is fractional and 2 is raised to that fractional power, which still gives a valid intermediate population size.
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Educational estimate, not medical advice — verify formulas, units and assumptions for your specific case.