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Doubling time

Doubling time is the time cell need to duplicate their population. This time should always be calculated during the log phase.

This is a graph which represents cell density on the Y-axis and days on the X-axis. At 0 days the lag phase starts and the cell density is around ten to the fourth. At day 3, the lag phase ends and the log phase starts. The cell density starts to increase. At day 8, the log phase ends and the cell density grew exponentially untilb reaching a value of ten to the sixth. The stationary phase starts and the cell density reaches a plateau until day 10. Right before and after the sixth day, two broken lines are drawn. The space between these two lines is labeled as doubling time.

Figure 1: Calculation of doubling time by interpolating the growth curve during the log phase.

While cells are in culture it is important to re-feed them frequently so they can proliferate at the same rate until they reach confluence at the stationary phase. Confluence is the ratio of the area occupied by cells to total available space and it is due to contact inhibition. This contact inhibition is mediated by the cell surface proteins. Therefore, in order to keep the culture at an optimal density for continued cell growth and to stimulate further proliferation, the culture has to be divided and fresh medium needs to be supplied. This is also called cell passaging or cell sub-culturing.

Referred from:

Article
Mammalian cell growth