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Cell Doubling Time Calculator

Calculate the doubling time of a cell population from an initial count, a final count and the time between them, assuming exponential growth.

Formula

Td=t ln⁡2ln⁡(Nt/N0)T_{\mathrm{d}} = \dfrac{t\,\ln 2}{\ln(N_t/N_0)}
doublings=log⁡2NtN0\text{doublings} = \log_2\dfrac{N_t}{N_0}
μ=ln⁡(Nt/N0)t\mu = \dfrac{\ln(N_t/N_0)}{t}
TdT_{\mathrm{d}}
doubling time
tt
time between the two counts
N0, NtN_0,\ N_t
cell number at the start and at time t

How it works

During exponential growth a population multiplies by a constant factor in each unit of time. The ratio of the final to the initial count gives the number of doublings, and the elapsed time divided by that number is the doubling time.

Both counts can be cells, cells/mL or cells/cm², as long as they use the same measure, because only their ratio enters the calculation.

Worked example

A culture grows from 2 × 10⁵ to 1.6 × 10⁶ cells in 72 hours.

  1. Nt / N₀ = 8, which is 3 doublings.
  2. Td = 72 h × 0.6931 / ln(8) = 24 h.

The doubling time is 24 hours.

These are the values the calculator opens with, so you can check its output against this example.

Assumptions

  • Growth was exponential for the whole interval, with no lag after seeding and no slowing near confluence.
  • Cell death during the interval is negligible.

Common mistakes

  • Including the lag phase. Counting from the moment of seeding overstates the doubling time.
  • Letting the culture reach confluence before the second count, which also overstates it.
  • Estimating from only two counts. A growth curve with several time points is more reliable.

Related tools

Population Doubling Level CalculatorPopulation doublings and cumulative PDL per passageOpen calculatorBacterial Growth Rate CalculatorSpecific growth rate and doubling timeOpen calculatorCell Confluence CalculatorEstimated confluence and time to reach a targetOpen calculatorHemocytometer Cell Counting CalculatorCells per mL from a hemocytometer countOpen calculator

Related equipment

Service documentation, failure modes and parts for the instruments this calculation is used with.