Enter the number of viable microorganisms before treatment and after treatment into the calculator to determine the log reduction and percent reduction.

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## Log Reduction Formula

The following formula is used to calculate a log reduction.

Log Reduction = log_{10 }(A/B)

Percent Reduction = (A-B) * 100 / A

- Where A is the number of viable microorganisms before treatment.
- B is the number of viable microorganisms after treatment.

## Log Reduction Definition

**What is a log reduction? **A log reduction is a simplified way of showing the reduction in microorganisms before and after a treatment. Using logs is useful because it reduces very large numbers to something manageable.

## Example Problem

How to perform log reduction?

**First, determine the number of microorganisms before treatment.**For this example, this value is 2,000,000.

**Next, determine the number of microorganisms after treatment.**After treatment there are only 500 microorganisms left.

**Finally, calculate the log reduction.**The log reduction is found to be: log10 ( A/B ) = 3.602.

## About Log Reduction

**Can a log reduction be negative? **If the number of microorganisms increases after treatment, the resulting log reduction will be negative. This means that there was actually an increase as opposed to a reduction, hence the negative value.

**What does 3 log reduction mean? **A 3 log reduction is equivalent to a 99.99% reduction in quantity, which in this case is quantity of microorganisms.

**What is 6 log reduction? **A 6 log reduction is equivalent to a 99.9999% reduction in a quantity.

**What is 5 log reduction? **A 5 log reduction is equal to 99.999% reduction.

**What is 4 log reduction? **A 4 log reduction is equal to 99.99% reduction.

**What is 2 log reduction? **A 2 log reduction is equal to 99% reduction.

**What is 1 log reduction? **A 1 log reduction is equal to 90% reduction.