GIFSQ Tools · Module 3 — Food Microbiology & Enumeration · Tool 041 of 500
Plate-count method. Enter the colonies counted, the volume plated and the total dilution factor to get the aerobic plate count in CFU per gram.
Try sample values — fills the form with the worked example below.
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CFU/g
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Log₁₀ CFU/g
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Scientific notation
Equation: CFU/g = C ÷ (V × d) · C = colonies counted, V = volume plated (mL), d = total dilution factor (for example 0.001 for 10⁻³). Log₁₀ CFU/g = log₁₀(CFU/g). Detection limit = 1 ÷ (V × d).
Method: Aerobic plate count, FDA BAM Chapter 3 / ISO 4833-1. Countable range 30 to 300 colonies per plate (FDA BAM). For a 10 g sample in 90 mL diluent the first dilution is 10⁻¹; multiply by each further 1:10 step to get the total dilution entered here.
Assumptions: each colony grew from one viable unit; the sample was mixed evenly; the dilution series was prepared correctly.
Limitations: counts below 30 or above 300 colonies are estimates, not reportable counts; clumps and chains count as one colony; injured cells may not grow on the medium used.
Rounding: CFU/g shown as a whole number; log₁₀ to 2 decimal places; intermediates unrounded. In a laboratory report, give CFU/g to 2 significant figures.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: Aerobic plate count, FDA BAM Chapter 3 / ISO 4833-1. Countable range 30 to 300 colonies per plate (FDA BAM). For a 10 g sample in 90 mL diluent the first dilution is 10⁻¹; multiply by each further 1:10 step to get the total dilution entered here.
Assumptions: each colony grew from one viable unit; the sample was mixed evenly; the dilution series was prepared correctly.
Limitations: counts below 30 or above 300 colonies are estimates, not reportable counts; clumps and chains count as one colony; injured cells may not grow on the medium used.
Rounding: CFU/g shown as a whole number; log₁₀ to 2 decimal places; intermediates unrounded. In a laboratory report, give CFU/g to 2 significant figures.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: 245 colonies counted on a plate with 1 mL plated at a total dilution of 10⁻³. CFU/g = 245 ÷ (1 × 0.001) = 245,000 CFU/g (2.45 × 10⁵ CFU/g), log₁₀ = 5.39. 245 colonies is inside the countable range.
Enter values above to see results.
Typical aerobic plate counts: pasteurised milk under 20,000 CFU/mL; ready-to-eat foods are often specified under 100,000 CFU/g — check the specification for the product. Tool 041 of 500 — GIFSQ
