Enter the number of colonies, dilution factor, and volume of the culture plate into the calculator to determine the bacterial concentration.

Bacterial Concentration Formula

The following formula is used to calculate a bacterial concentration. 

BC = C * DF / VC
  • Where BC is the bacterial concentration (cfu/ml)
  • #C is the number of colonies
  • DF is the dilution factor
  • VC is the volume of the culture plate (ml)

To calculate a bacterial concentration, multiply the number of colonies by the dilution factor, then divide by the volume of the culture plate.

What is a bacterial concentration?

A bacterial concentration is a measure of the total number of bacteria per unit of weight or volume. This is typically measured in colony-forming units per milliliter of culture.

How to claculate bacterial concentration?

The following example problem outlines the steps needed to calculate a bacterial concentration.

First, determine the number of colonies. In this example, the number of colonies is 50.

Next, determine the dilution factor. This solution is diluted by a factor of 1:2 = .5.

Next, determine the total volume of the culture plate. In this case, the total volume is 20ml.

Finally, calculate the bacterial concentration using the formula above:

BC = #C * DF / VC

BC = 50 * .5 / 20

BC = 1.25 CFU/ml