Calculate percent defective, quality yield, defective parts per million, defects per unit, or DPMO from inspected units, defect counts, and opportunities per unit.

Count each defective unit once, even when it has multiple defects.

Defect Rate Formula

The following formula is used to calculate the defect rate of a product.

DR = TD / UT × 100
  • Where DR is the defect rate (%)
  • TD is the number of defective units, counting each unit once even if it has multiple defects
  • UT is the total number of units tested for defects

To calculate percent defective, divide defective units by inspected units and multiply by 100. For individual defect occurrences, use DPU = defects / units; DPMO = defects / (units × opportunities per unit) × 1,000,000.

What is a defect rate?

Definition:

Percent defective is the percentage of inspected units with at least one defect. Defects per unit counts individual defect occurrences and may exceed one; it is not the percentage of defective units.

There are two different ways to look at the defect rate. One way is that a product is simply defective or not. In this case, any defect in the product would make the entire product defective. The other way is that each product can have more than one defect.

Each method has its uses in determining the causes of defects in products and the severity.

How to calculate a defect rate?

Example:

The following example provides the steps and information required to calculate a defect rate of a product.

First, determine the total number of units that are being observed or checked for defects. In this example problem, there are 1000 units tested for defects.

Next, count defective units once each. For this example, 25 of the 1,000 inspected units were defective, regardless of how many individual defects each had.

Finally, calculate the defect rate using the formula above:

DR = TD / UT *100

DR = 25 / 1000*100

DR = 2.5 %