At high quality, percentages are too coarse — 0.05% sounds tiny but is 500 PPM. Parts-per-million expresses defect rates at the precision modern manufacturing and Six Sigma demand.
The example
60 defects of 200,000.
| A | B | |
|---|---|---|
| 1 | Item | Value |
| 2 | 60 / 200,000 | — |
| 3 | PPM | → 300 |
The formula
The formula:
How it works
How it works:
- Compute the defect fraction (defects ÷ total) and multiply by 1,000,000.
- PPM gives meaningful resolution at high quality — where percentages round to zero.
- Convert back:
PPM / 10000= percent (300 PPM = 0.03%). - Six Sigma targets 3.4 PPM — the famous defects-per-million-opportunities benchmark.
PPM vs DPMO. Plain PPM counts defective units per million. DPMO (defects per million opportunities) divides by units × opportunities-per-unit — better when one unit can fail multiple ways. For a single pass/fail check they coincide; for complex assemblies, DPMO normalizes across products with different defect opportunities, which is what Six Sigma scoring uses.
Try it: interactive demo
Defects and total units.
Variations
PPM to percent
Convert back:
DPMO
Per opportunity:
Defects at a PPM target
Allowed defects:
Pitfalls & errors
Times a million. Don’t forget the ×1,000,000 scaling.
PPM vs DPMO. Divide by opportunities, not just units, for complex parts.
Big samples. PPM needs large counts to be meaningful — 1 of 100 is a noisy 10,000 PPM.
Practice workbook
Frequently asked questions
How do I calculate defects in PPM in Excel?
How do I convert PPM to a percentage?
What's the difference between PPM and DPMO?
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