Calculator
Example data table
| Batch | Inspected | Defects | Defect % | PPM | Status |
|---|---|---|---|---|---|
| B-2401 | 1,000 | 9 | 0.90% | 9,000 | Pass |
| B-2402 | 1,200 | 18 | 1.50% | 15,000 | Pass |
| B-2403 | 800 | 22 | 2.75% | 27,500 | Fail |
| B-2404 | 1,500 | 12 | 0.80% | 8,000 | Pass |
Formula used
- Defect % = (Total Defects ÷ Units Inspected) × 100
- PPM = (Total Defects ÷ Units Inspected) × 1,000,000
- Yield % = ((Units Inspected − Total Defects) ÷ Units Inspected) × 100
- DPMO = (Total Defects ÷ (Units Inspected × Opportunities per Unit)) × 1,000,000
- Sigma (approx.) = NORMSINV(1 − DPMO/1,000,000) + 1.5
- Weighted score % = ((C×wC + M×wM + m×wm) ÷ Units Inspected) × 100
How to use this calculator
- Enter your batch name, units inspected, and total defects found.
- Select the threshold type you manage (percent, PPM, or count).
- Set the threshold value and submit to get Pass/Fail.
- Optionally enable AQL and category limits for stricter control.
- Use opportunities per unit to compare processes via DPMO.
- Download CSV or PDF after each calculation for reporting.
Quality thresholds that drive consistent release decisions
A defect threshold checker converts inspection findings into a repeatable accept or reject decision. When you standardize the limit by percent, PPM, or count, you reduce debate. For example, a 2.00% limit on 1,200 inspected units allows up to 24 defects, while a 15,000 PPM limit allows 18 defects on the same sample. Consistent rules make comparisons meaningful across lines and suppliers.
Connecting AQL targets with operational metrics
AQL is often defined in agreements, but daily management benefits from converting it into a measurable defect rate. If your AQL is 1.50%, the calculator flags any batch above that level even when a broader threshold passes. This dual check protects customer commitments while supporting internal capability work. Pairing AQL with yield highlights cost: at 1.50% defects, yield is 98.50%, which impacts scrap and rework.
Why severity categories improve risk control
Not all defects carry the same risk. Category limits prevent a “good-looking” overall rate from masking critical failures. A batch may pass a 2.00% total limit but still be rejected if critical defects exceed 0.20% or if a count cap is breached. This aligns inspection outcomes with safety, compliance, and warranty exposure. Using category mode also clarifies which corrective actions deliver the biggest risk reduction.
Using DPMO and sigma as comparability signals
DPMO normalizes defects by opportunities per unit, enabling fair comparisons across products with different complexity. If you inspect 1,200 units with four opportunities each and find 18 defects, DPMO is 3,750. The calculator estimates long-term sigma using a standard normal approximation plus a 1.5 shift. While sigma is an estimate, it is a consistent indicator for tracking improvement, validating process changes, and comparing suppliers.
Reporting and continuous improvement workflows
Exporting CSV and PDF keeps decisions traceable. Use the CSV to build dashboards showing defect percent, PPM, and category pass rates. Use the PDF as an audit attachment for lot release, supplier claims, or CAPA records. A simple routine is to review three things each batch: overall status, category status, and trend versus the prior three lots. When the same rule set is applied consistently, the data stays actionable and discussions remain objective.
FAQs
1) What is the difference between defect percent and PPM?
Defect percent is defects per 100 inspected units. PPM scales the same ratio to one million units, which is useful when defects are rare and you want finer sensitivity for targets and trend tracking.
2) When should I use a count threshold instead of a percent threshold?
Use count thresholds when your sampling plan or contract states a maximum number of defects for a specific inspected quantity. Percent thresholds are better for comparing lots with varying inspection sizes.
3) Do I have to fill in critical, major, and minor defects?
No. You can run the calculator with only total defects. Enter category defects only when you want severity-based reporting, weighted scoring, or per-category acceptance rules.
4) How should I choose opportunities per unit?
Use the number of defect opportunities defined in your control plan, such as inspection points, features, or CTQs. Keep it consistent across batches for the same product family to compare DPMO properly.
5) Is the sigma value an official Six Sigma certification result?
No. It is an estimate derived from DPMO using a standard normal approximation and a 1.5 shift. It helps compare process performance, but it does not replace formal capability studies.
6) Why can a batch fail even if the overall threshold passes?
Optional rules can override the overall result. If AQL is set and exceeded, or if a category limit is breached, the calculator marks the batch as Fail to reflect higher risk tolerance requirements.