What this calculator does
Log reduction (microbial kill) works out how many orders of magnitude a treatment reduces a microbial count. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaLog reduction = log₁₀(N₀/N); % reduction = (1 − N/N₀) × 100
The inputs explained
| Field | What to enter |
|---|---|
| Initial count (CFU) | A number, measured in CFU. Starts at 1000000. |
| Final count (CFU) | A number, measured in CFU. Starts at 10. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with initial count
Every other input is held at the calculator’s starting values while initial count varies. Select any row to load that scenario into the calculator.