Log Reduction Calculator

Your details

Choose what you want to calculate. All three modes use the same underlying formula.
Quick presets pre-fill typical initial counts and target log reductions used in regulatory and industry standards.
The unit label is shown in results. All calculations are unit-independent.
The number of colony-forming units before treatment. Enter the actual count, not the log value.
The number of colony-forming units remaining after treatment. Must be less than or equal to the initial count.
If you enter the treatment time, the calculator will compute the D-value: the time to achieve a 1-log (90%) reduction. Leave at 0 to skip.
min
Lowest detectable count. If the final count is below this, the calculator uses this value as a conservative floor for SAL.
Log₁₀ ReductionHigh-level disinfection
6log

Base-10 log of the ratio of initial to final microbial count

Percent kill1%
Percent remaining0.000001%
Survival fraction10^-6.00 (1.00e-6)
Final count1CFU/mL
Initial count1,000,000CFU/mL
SAL (probability of non-sterility)1.0000
Reduction categoryHigh-level disinfection (5-log)
6 log
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6.00-log reduction: High-level disinfection (5-log)

  • A 6.00-log reduction eliminates 99.9999% of organisms, leaving 0.000100% behind.
  • Starting from 1.00e+6 CFU/mL, the treatment reduces the count to approximately 1.00e+0 CFU/mL.

Next stepTo reach sterilization assurance (6-log), increase exposure time, concentration, or temperature. Use the D-value to estimate the additional treatment time needed.

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