Enter the time, initial quantity, and final quantity into the calculator to determine the D-Value.

## D Value Formula

The following formula is used to calculate a D Value.

D = t / [ log_{10 }(Q1) – log_{10} (Q2) ]

- Where D is the d-value
- t is the total time that has passed
- Q1 is the initial quantity
- Q2 is the final quantity

## D Value Definition

**What is a d-value? **A d-value is a term used to describe the total time it takes to reduce a quantity by 1 log factor, or 90%. This value is most often used in biology to measure decreases in microorganisms over time, but it can also be used in other statistical analysis.

## Example Problem

How to calculate d-value?

**First, measure the initial quantity.**For this example, the initial quantity is 1,000,000.

**Next, determine the total time.**Measuring the total time in this case yields 30 minutes.

**Next, determine the final quantity.**The final quantity is measure to be 3,000 after 30 minutes.

**Finally, calculate the d value.**Using the formula above, the d value is found to be 30 / (log 1,000,000) – log ( 3,000) = 11.89 minutes