GIFSQ Tools · Module 3 — Food Microbiology & Enumeration · Tool 047 of 500
Convert between a plate count and its base-10 logarithm, both ways. Enter either the count or the log value — the other is calculated.
Try sample values — fills the form with the worked example below.
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Count (CFU)
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Log₁₀ value
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Scientific notation
Equation: log₁₀(CFU) = log₁₀(count) · count = 10^(log₁₀ value).
Method: Base-10 logarithm conversion, as used for reporting plate counts in FDA BAM and ISO 7218 — counts are commonly reported as log₁₀ CFU/g. If both fields are entered, the count is used.
Assumptions: the count is a positive number; the log value refers to the same basis (per gram or per millilitre) as the count.
Limitations: log₁₀ is not defined at zero — a zero count is below the detection limit and cannot be converted; logs compress large differences, so a small log difference still means a large count difference.
Rounding: log₁₀ to 3 decimal places; the count as a whole number; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: Base-10 logarithm conversion, as used for reporting plate counts in FDA BAM and ISO 7218 — counts are commonly reported as log₁₀ CFU/g. If both fields are entered, the count is used.
Assumptions: the count is a positive number; the log value refers to the same basis (per gram or per millilitre) as the count.
Limitations: log₁₀ is not defined at zero — a zero count is below the detection limit and cannot be converted; logs compress large differences, so a small log difference still means a large count difference.
Rounding: log₁₀ to 3 decimal places; the count as a whole number; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: 250,000 CFU/g converts to log₁₀ 250,000 = 5.398. The other way, a log₁₀ value of 5.40 converts to 10^5.40 = 251,189 CFU/g.
Enter values above to see results.
A 1-log change is a 10-fold change in count: 250,000 CFU/g is log₁₀ 5.40. Keep the basis (per gram or per millilitre) the same on both sides of a conversion. Tool 047 of 500 — GIFSQ
