CFU / Plating Calculator
CFU/mL = colonies / (plated volume × dilution fraction)
Convert colony counts into CFU/mL using the plated volume and the dilution fraction you entered.
Inputs
0 = undiluted. The cumulative dilution fraction is shown in the working.
Calculation
Definition
CFU/mL = colonies / (plated volume in mL × dilution fraction)
Replicate handling
3 plate(s): 142, 156, 138 — arithmetic mean of the replicate counts
representative count = 145.333
Substitution
145.333 / (0.1 mL × 0.0001)
1.45333 × 10^+7 CFU/mL
Inputs
- Colony counts
- 142, 156, 138
- Averaging
- mean
- Plated volume
- 100 µL
- Dilution fraction
- 0.0001
This is arithmetic only. LabCalc does not apply countable-range rules, plate-acceptance criteria or any regulatory microbiology method.
The dilution fraction is the cumulative fraction of the original suspension on the plate (10⁻⁴ = 0.0001).
About this calculator
The viable count of a suspension is the number of colonies on the plate divided by the volume plated and the fraction of the original suspension that volume represents. Enter the dilution as a power of ten: 4 means a 10⁻⁴ dilution.
This is arithmetic only. LabCalc applies no countable-range rule, no plate acceptance criterion and no microbiological standard — those belong to your method. How replicate plates are combined is your explicit choice and is recorded in the result.
LabCalc is provided as a calculation aid. Users remain responsible for verifying calculations, units, chemical compatibility, experimental procedures and applicable safety requirements before laboratory use.
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