Cell Doubling Time Calculator
Doubling time and growth rate from two cell counts — with the number of divisions and the projection forward.
Exponential growth between two counts gives the doubling time as t × ln2 ÷ ln(N/N₀).
How the cell doubling time calculator works
Exponential growth between two counts gives the doubling time as t × ln2 ÷ ln(N/N₀). The number of population doublings is log₂(N/N₀).
It only holds while growth is exponential. Cultures leave that phase as they approach confluence or exhaust the medium, and a doubling time measured across that transition understates the true rate badly.
Formula: Td = t × ln2 / ln(N/N₀)
Worked examples
| Inputs | Doubling time | Note |
|---|---|---|
| 100k to 800k in 48 hours | 16 hours | exactly 3 doublings, 16 hours each |
| A slower line | 30.285 hours | about 30 hours |
| A fast bacterial culture | 1.003 hours | about 1 hour |
FAQFrequently asked questions
What is doubling time?
The time for a population to double. It is the natural way to express exponential growth rate for cells.
How do I calculate it?
Elapsed time multiplied by ln 2, divided by the natural log of the fold change.
What is a typical doubling time?
E. coli manages about 20 minutes in rich medium; mammalian cell lines are typically 18 to 24 hours; primary cells often far longer.
Why does my measured time vary?
Because growth is only exponential in one phase. Measuring across the lag phase or into confluence gives a longer apparent doubling time than the true one.
What is the specific growth rate?
μ, the exponential rate constant. Doubling time is ln 2 divided by it — the same relationship as radioactive half-life.
Where these figures come from
- NCBI Bookshelf — Molecular Biology of the Cell — growth kinetics and molecular conventions
- CSIRO — Australia's national science agency
Last checked: September 2026. Formulas are the standard textbook forms; assumptions are stated on each page because they are where these models break.