Cell counting/plating

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Count the number of viable cells in a culture via dilution plating. The following assumes E. coli cells but it should apply to any type of cells.


  • LB agar plate
  • LB media for dilution
  • 8-tube strips (optional but easiest)


  1. Fill each tube in the dilution with 90 μl of LB
  2. Add 10 μl of the sample to the first tube and mix
  3. From the first tube, remove 10 μl and mix into second tube
  4. Repeat for the number of dilutions you wish to do (8 should be more than enough)
  5. Take 10 μl from each dilution and spot it on to the agar plate
  6. Allow droplet to dry and incubate

The first dilutions will contain a thick lawn of cells and the last dilutions will contain no cells. There should be one drop which contains countable single colonies. From this, you can calculate the number of cells in the original sample. For example, if there 4 colonies on dilution 5, there are 4E4 cells/μl.