What This Calculator Does
Log reduction is a standard way to express how much a microbial (or other particle) population has been reduced by a disinfection, sterilization, or filtration process.
The Formula
Log reduction is calculated as log10(N0 / N), where N0 is the initial count and N is the final count. Each whole log reduction represents a 90% decrease: a 1-log reduction means 90% fewer organisms remain, a 3-log reduction means 99.9% fewer, and so on.
- Enter the initial count before treatment.
- Enter the final count after treatment.
This calculator is intended for general educational and lab-reference use. For regulated disinfection validation studies, follow the specific test methods and acceptance criteria required by the relevant standard or authority.
Last reviewed August 2026