How is the final dilution factor calculated in serial dilution?

The final dilution factor in a serial dilution is calculated by multiplying the individual dilution factors of each step. 

Final dilution factor (FDF) = sample dilution factor (SDF) * total series dilution factor (TSDF) * plating dilution factor (PDF). 

As an example, the FDF would equal 1/4000 if the values of SDF, TSDF, and PDF  were ½ , 1/600 , 3/10, respectively. This means that the initial sample in tube III was 4000 times more concentrated compared to the plated sample. In simpler terms, one would need 4 liters of the sample taken from tube 1 to have the same quantity of bacteria as 1 mL of the original sample.