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(Q1) -  log(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

To calculate a d-value, subtract the log base 10 of the final quantity from the log of the initial quantity, then divide the total time by this result.

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 analyses.

Example Problem

How to calculate d-value?

  1. First, measure the initial quantity.

    For this example, the initial quantity is 1,000,000.

  2. Next, determine the total time.

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

  3. Next, determine the final quantity.

    The final quantity is a measure to be 3,000 after 30 minutes.

  4. 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