Cell doubling time calculator
Enter the starting cell count, the count later on and the time in between to get the doubling time, the growth rate, the number of doublings and the fold increase. Or switch modes and enter a known doubling time to predict how many cells you will have after a given time.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Choose the doubling time (from two counts) or the count later on (from a known doubling time).
- Enter the starting count and either the final count or the doubling time.
- Enter the time elapsed and its unit: minutes for bacteria, hours or days for cultured cells.
- Read the doubling time, the growth rate and the number of doublings.
- Doubling time: Td = t × ln 2 ÷ ln(N ÷ N₀)
- Number of doublings: n = log₂(N ÷ N₀) = t ÷ Td
- Growth rate: r = ln(N ÷ N₀) ÷ t = ln 2 ÷ Td
- Count later: N = N₀ × 2^(t ÷ Td)
Worked example
A flask is seeded with 100,000 cells and holds 800,000 after 72 hours. N ÷ N₀ = 8, ln 8 = 2.0794, so Td = 72 × 0.6931 ÷ 2.0794 = 24 h: three doublings, one per day, and a growth rate of 0.028881 per hour.
Bacteria that double every 20 minutes, starting from 1,000 cells: after 120 minutes, 120 ÷ 20 = 6 doublings and 1,000 × 2⁶ = 64,000 cells.
Tips
- Count carefully. A 10 % counting error in N changes the doubling time by several percent; average several counts.
- Exponential phase only. The formula assumes steady growth; it does not describe lag or plateau phases.
- Population doublings in passaging. For a whole culture history, add the doublings of each passage: log₂(cells harvested ÷ cells seeded).
Frequently asked questions
How do you calculate doubling time?
For exponential growth, Td = t × ln 2 ÷ ln(N ÷ N₀), where N₀ and N are the counts at the start and after time t. If 100,000 cells become 800,000 in 72 hours, that is 8-fold = 3 doublings, so Td = 72 ÷ 3 = 24 hours.
What is the specific growth rate?
The constant r in N = N₀ × e^(r × t): r = ln(N ÷ N₀) ÷ t, per hour or per day. It relates to the doubling time by r = ln 2 ÷ Td, so a 24-hour doubling time is r = 0.028881 per hour.
Can I use confluence or optical density instead of counts?
Yes, any measure proportional to the number of cells works, because only the ratio N ÷ N₀ matters. Optical density is proportional to cell number only over a limited range, and confluence only while cells still have room.
Why is my doubling time longer than the published one?
Cells first adapt after seeding (lag phase) and slow down as they approach confluence or run out of nutrients. Take both counts during the exponential phase, for example 24 h after seeding and a day or two later.