For any exponentially growing culture, take a measurement of the number of cells at an initial time (N
_{i}), and a second measurement at some later time (N
_{L}). If T is the length of time between the observations:
doubling time = T ⋅ ln(2) / ln(N_{L} / N_{i}) measured in units of T.
example:
at 4:00 pm on Monday, 3 x 10^{5} cells are plated. At 3:00 pm the following Friday, 2.5 x 10^{6} cells are counted.
- N_{i} = 3 x 10^{5}
- N_{L} = 2.5 x 10^{6}
- T = 95 hours
The doubling time for this culture would be:
- 95 ⋅ ln(2) / ln( 2.5 x 10^{6} / 3 x 10^{5}) = 31.1 hours ≃ 1.3 days
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