Work out colony forming units instantly with clear inputs, formula shown and shareable results.
Multiplies the colony count by the dilution factor and divides by the volume plated to give viable counts per millilitre.
Viable count
CFU/mL = colonies counted x dilution factor / volume plated (mL)
Below 30 the Poisson error is large; above 300 colonies merge and are undercounted.
One colony may arise from a clump of cells, so the count measures viable units rather than individual cells.