Cell doubling time calculator
Maintained by the Talindrew team · Last updated
Doubling time is the time a population needs to double under exponential growth: Td = t × ln 2 / ln(Nt/N0), from a starting count N0, a final count Nt and the elapsed time t. Growing from 1 × 10⁵ to 8 × 10⁵ cells in 72 hours is three doublings: a 24-hour doubling time.
Result
Td = t × ln 2 / ln(Nₜ/N₀), assuming exponential growth throughout. 1×10⁵ → 8×10⁵ in 72 h is exactly three doublings → Td = 24 h. Counts from confluent or lagging cultures violate the exponential assumption.
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What it looks like
Formula
Td = t × ln 2 / ln(Nₜ/N₀)
Source: Exponential growth kinetics (ATCC animal-cell culture guidance)
Worked example
Given: Seeded 1 × 10⁵ cells; counted 8 × 10⁵ cells 72 h later
- 1.Fold growth: 8 × 10⁵ / 1 × 10⁵ = 8 = 2³ → three doublings.
- 2.Td = 72 × ln 2 / ln 8 = 72 / 3 = 24 h.
Doubling time = 24 hours
How the calculation flows
Units & constants
| Typical HEK293 / CHO | ~20–30 h |
|---|---|
| Typical HeLa | ~24 h |
| E. coli (LB, 37 °C) | ~20–30 min |
| S. cerevisiae (YPD, 30 °C) | ~90 min |
| Assumption | Exponential (log-phase) growth throughout the interval |
| Price | Free |
When is the calculation valid?
Only across the exponential phase. Counts taken during the post-seeding lag, at confluence, or after a medium change spanning starvation give a blended number that understates true growth rate. Count at two points where the culture is visibly sub-confluent and actively dividing, and use viable counts (trypan blue or equivalent): dead cells in the denominator corrupt the ratio.
What is doubling time used for?
It is the planning constant of routine culture:
- Predicting when a flask reaches the target density for passage or transfection.
- Detecting drift: a line whose Td lengthens over passages is stressed, contaminated or senescing.
- Comparing growth under treatments; many drug effects report as Td shifts.
- Back-calculating seed density: to reach 10⁶ cells in 3 days at Td 24 h, seed 1.25 × 10⁵.
Frequently asked questions
Td = 72 × ln 2 / ln 10 = 72 × 0.693 / 2.303 = 21.7 hours: 10-fold is 3.32 doublings.
Not exactly. Population doubling time includes cells that die or arrest; individual cycling cells divide slightly faster than the population doubles. For healthy log-phase cultures the difference is small.
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