Calculate the log₁₀ reduction, percent reduction, and fold reduction from counts before and after a kill step.
| Log10 reduction | – |
| Percent reduction | – |
| Fold reduction | – |
Use this calculator to quantify how far a disinfection, pasteurisation, or biocide step reduced a microbial or molecular count. Enter the count before treatment and the count remaining afterwards.
The calculation is: log reduction = log₁₀(initial ÷ remaining). Percent reduction is (1 − remaining ÷ initial) × 100. Fold reduction is initial ÷ remaining. A 1-log drop is a 10-fold (90%) reduction; a 3-log drop is a 1,000-fold (99.9%) reduction.
Both counts must be greater than zero. A true remaining count of zero cannot be expressed as a finite log reduction; it means the reduction is greater than the logs implied by the assay's detection limit. Remaining cannot exceed the initial count.
Initial count: The count before treatment, in the same units as the remaining count (CFU, cells, copies, or any other consistent count).
Remaining count: The count after treatment. Must be above zero and not greater than the initial count.
Log10 reduction: The base-10 log drop. Dimensionless.
Percent reduction: The same drop expressed as a percentage of the initial count.
Fold reduction: How many times smaller the remaining count is than the initial count.
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