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Defect rate calculator
Enter how many defects you found and how many units you checked to get the defect rate, the yield, and the DPMO used in quality reporting.
Leave opportunities per unit at 1 for a simple pass/fail rate; raise it only when one unit can fail in several ways.
How the defect rate is calculated
The defect rate is the number of defects divided by the number of units inspected, written as a percentage. With 8 defects in 500 units the rate is 8 ÷ 500 = 0.016, or 1.6%. The yield is the mirror image, the share that passed: 100% − 1.6% = 98.4%. Both describe the same batch from opposite directions.
For Six Sigma reporting, quality is measured in defects per million opportunities, or DPMO. An opportunity is a single way a unit could fail, so a form with three fields that must each be correct has three opportunities. DPMO = defects ÷ (units × opportunities) × 1,000,000. With 8 defects, 500 units and 1 opportunity each, that is 8 ÷ 500 × 1,000,000 = 16,000 DPMO. Counting opportunities lets you compare a simple part with a complex one on a fair footing.
| Defect rate | DPMO (1 opp.) | Yield |
|---|---|---|
| 10% | 100,000 | 90% |
| 1% | 10,000 | 99% |
| 0.1% | 1,000 | 99.9% |
| 0.01% | 100 | 99.99% |
Using the result
Judge the rate against your own history and the cost of each defect, not a universal target. A 2% defect rate on greeting cards and on parachute cords mean very different things. The most useful next step is almost never to inspect harder; it is to find the handful of causes behind most defects, because quality problems usually follow a Pareto pattern where roughly 20% of causes create 80% of the defects.
Be consistent about what counts as a defect and what counts as a unit, or the rate will drift for reasons that have nothing to do with the process. Defects per unit can exceed one when a single item has several faults, which is why the calculator keeps defects and opportunities separate. If you only track pass or fail at the unit level, leave opportunities at one and read the straightforward percentage.
Frequently asked questions
What is the difference between defect rate and DPMO?
Defect rate is defects divided by units, shown as a percent. DPMO scales defects by the number of opportunities per unit and expresses the result per million, so complex and simple items can be compared fairly.
How do I count opportunities per unit?
Count the distinct ways one unit can fail, such as each critical dimension, field or feature that must be correct. If a unit either passes or fails as a whole, there is one opportunity.
Is a lower defect rate always worth it?
Only up to the point where prevention costs less than the defects it avoids. Weigh the cost and consequence of each defect; cutting a rate that already costs little may not pay for itself.