Determine the period of time to be used for computing the generation time of the bacteria. This can range from a few minutes to a couple of hours.
Search for data indicating how much the bacteria have grown in the period of time defined during the previous step. The most common way to do this is to count the number of cells that have grown over the period.
Calculate the number of generations by computing log base 2 of the growth number from the previous step. For example, if there was an increase of 64 in the number of cells, then the number of generations would equal log base 2 of 64, or 6. This formula is used because during the exponential phase, the quantity doubles with each generation time.
Use the formula "generation time = time elapsed / number of generations" to compute the generation time during the exponential phase. If, for the example above, the increase of 64 was noticed in an interval of one hour, the generation time would be 1 hour / 6 = 10 minutes.