Defects per unit (DPU) is the first metric to calculate and the easiest to explain to anyone on the line. DPU = total defects ÷ total units inspected. A DPU of 0.024 means that, on average, every card carries 0.024 defects, or put another way, you expect about 24 defects in every 1,000 cards.
DPU is useful because it tracks the line without needing the opportunity count. Operators can plot it on a run chart at the end of every shift. Its weakness is that it cannot compare products of different complexity. A card with 10 cavities and a card with 30 cavities might both show a DPU of 0.024, but the 30-cavity card has three times as many places to go wrong and is therefore performing better per opportunity. That is the gap DPO and DPMO fill.
Key Concept
DPU = defects ÷ units; it is the quickest shop-floor measure but ignores product complexity.
Practical Example
Over one week the line produces 2,500 ten-cavity cards for a single product, and inspection logs 60 defects: 38 empty or broken tablets, 15 seal faults and 7 print faults. DPU = 60 / 2,500 = 0.024 defects per card. Plotted next to the previous week's 0.031, the line is improving, and the breakdown by type shows tablet feed as the biggest contributor.
Standard Procedure
- 1Total the defects found in the period from the inspection log.
- 2Total the units inspected in the same period.
- 3Divide defects by units to get DPU.
- 4Break the defect total down by type so the largest category is visible.
Lesson Summary
- ✓DPU is simple and good for tracking one product over time.
- ✓DPU cannot fairly compare products with different numbers of opportunities.