Log Reduction Calculator
Measure the efficacy of a sterilization, disinfection, or sanitation process. Compare pre-treatment and post-treatment microbial population counts.
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Colony Forming Units (CFUs)
Input pre-treatment and post-treatment counts.
Calculated Log Reduction
5.0 log
* A 5-log reduction indicates a 99.999% microbial reduction.
Percent Reduction 99.999%
Survival Fraction 0.00001 (1 in 100,000)
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Expert Tip
In food safety and pharmaceutical manufacturing, a "5-log reduction" (99.999%) is the standard validation threshold for microbial kill rates.
Methodology & Log Reductions
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The Log Reduction Equation
Log reduction is calculated as the base-10 logarithm of the ratio of initial CFUs to final CFUs:
Log Reduction = log10(N0 / Nf)
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Reduction Scale Reference
| Log Reduction | Percent Reduction |
|---|---|
| 1-log | 90% |
| 2-log | 99% |
| 3-log | 99.9% |
| 4-log | 99.99% |
| 5-log | 99.999% |
How to Calculate Log Reduction and Percent Kill
Log reduction measures how effectively a disinfection process reduces contamination:
1
Determine Initial Count (N0)
Note the concentration of microorganisms before treatment.
2
Determine Post-Treatment Count (N)
Note the surviving microbial count.
3
Apply the Formulas
Log Reduction = log10(N0 / N). Percent Reduction = (1 - N / N0) × 100%.