# Cell doubling time calculator

> Calculate population doubling time and growth rate from two cell counts, or fit a growth curve over the exponential phase with R². Chart and CSV. Free.

URL: https://www.labcanvas.com/tools/cell-doubling-time-calculator

Doubling time Td = t × ln 2 / ln(N / N₀), where N₀ and N are the cell counts at the start and end of an interval t in exponential growth. Enter two counts and the time, or paste a growth curve to fit ln(N) against time, and get the doubling time, growth rate and doublings per day.

## Quick answer

- **What it does:** Calculates the population doubling time and growth rate from two cell counts, or from a growth curve fitted over the exponential phase with R².
- **Formula:** Td = t × ln 2 ÷ ln(N ÷ N₀); µ = ln(N ÷ N₀) ÷ t = ln 2 ÷ Td.
- **Example:** 100,000 cells growing to 400,000 in 48 h: Td = 48 × 0.693 ÷ ln 4 = 24 h (two doublings), µ = 0.0289 per hour.

Free, in the browser, no account needed. Updated 2026-11-08.

## Features

- From two counts or a full growth curve
- Specific growth rate \(\mu\) and doublings per day
- Log-linear fit with R² and a chart
- Minutes, hours or days

## How to use it

1. **Enter your counts**: Type the initial and final count and the time between them, or paste time and count columns from a growth curve.
2. **Use the exponential phase**: Leave out lag-phase and plateau points; the fit’s R² shows whether growth was exponential.
3. **Read the result**: Get the doubling time in the unit you want, the growth rate, and a chart of the fit.

## At a glance

| | |
| --- | --- |
| Formula | \(T_\mathrm{d} = \ln 2 / \mu\), \(\mu = \ln(N / N_0) / t\) |
| Input | Two counts, or a growth curve (any measure proportional to cell number) |
| Fit | Least squares on \(\ln N\) against time, with R² |
| Output | Doubling time in minutes, hours or days; chart (PNG, SVG) and CSV |

## How it works

$$N = N_0 \cdot e^{\mu t}$$

$$\mu = \frac{\ln(N / N_0)}{t}$$

$$T_\mathrm{d} = \frac{\ln 2}{\mu} = \frac{t \cdot \ln 2}{\ln(N / N_0)}$$

For a growth curve the slope of \(\ln(N)\) against time is fitted by least squares; that slope is \(\mu\). Any measure proportional to cell number works (cells/mL, confluence, OD, luminescence), as long as all points use the same one.

## Worked example

100,000 cells grow to 400,000 in 48 h: \(T_\mathrm{d} = 48 \times 0.693 / \ln 4 = \mathbf{24\ h}\), two doublings, \(\mu = 0.0289\) per hour.

## Questions

### How do you calculate cell doubling time?

Count the cells at two time points during exponential growth and use \(T_\mathrm{d} = t \times \ln 2 / \ln(N/N_0)\). For example, 4-fold growth in 48 hours is two doublings, so \(T_\mathrm{d} = 24\) hours.

### What is the difference between doubling time and generation time?

For a population growing exponentially they are the same number. Generation time is the cell-cycle length of individual cells; population doubling time can be longer if some cells do not divide or die.

### Why do I need the exponential phase?

In lag and stationary phases growth is not exponential, so including those points underestimates the growth rate and overestimates the doubling time.

### What are typical doubling times?

Escherichia coli can double in about 20 minutes in rich medium, budding yeast in about 90 minutes, and common mammalian cell lines such as HeLa or HEK293 in roughly 20–30 hours.