Log Reduction Calculator

Find log reduction and percent kill of a population.

Log reduction 4

Percent reduction (%) 99.99

Formula: log reduction = log₁₀(initial ÷ final)

Step-by-step with your numbers:

1. Values used:

2. Initial count = 1,000,000 CFU

3. Final count = 100 CFU

5. Log reduction = 4

6. Percent reduction = 99.99%

Did we solve your problem today?

Measure how effectively a treatment reduces a microbial population.

The math behind it

log reduction = log₁₀(initial ÷ final). Each whole log is a 10× reduction (1 log = 90%, 2 logs = 99%, 3 logs = 99.9%).

1,000,000 → 100 → 4-log reduction (99.99%).

Disinfectant claim?

A '5-log kill' means 99.999% of organisms eliminated.