Sigma level measures how good your process is at avoiding defects. Here's exactly how to calculate it — with the DPMO formula, a reference table, and worked examples.
Sigma level tells you how many standard deviations fit between your process mean and the nearest specification limit. The higher the sigma level, the fewer defects you produce.
The scale runs from 1σ (about 690,000 defects per million) to 6σ (just 3.4 defects per million). Most organisations operate at around 3–4σ without active improvement.
Follow these four steps:
Worked example: 500 invoices inspected, 38 defects found, 4 opportunities per invoice. DPMO = (38 ÷ (500 × 4)) × 1,000,000 = 19,000 DPMO ≈ 3.6σ
Use the Sigma Level Calculator →Use this table to convert DPMO to sigma level:
| Sigma Level | DPMO | Yield |
|---|---|---|
| 1σ | 690,000 | 30.9% |
| 2σ | 308,537 | 69.1% |
| 3σ | 66,807 | 93.3% |
| 4σ | 6,210 | 99.4% |
| 5σ | 233 | 99.98% |
| 6σ | 3.4 | 99.9997% |