Calculator
Example data
| Supplier | Units inspected | Scrap | Rework | Defective units | Unit defect rate | PPM |
|---|---|---|---|---|---|---|
| Northline Components | 1,000 | 12 | 8 | 20 | 2.000% | 20,000 |
| Atlas Fasteners | 2,500 | 6 | 4 | 10 | 0.400% | 4,000 |
| Prime Plastics | 750 | 9 | 0 | 9 | 1.200% | 12,000 |
Formula used
Unit defect rate
Defective units = Scrap units + (Rework units if included)
Unit defect rate (%) = (Defective units ÷ Units inspected) × 100
PPM = (Defective units ÷ Units inspected) × 1,000,000
Lot defect rate
Lot defect rate (%) = (Defective lots ÷ Lots received) × 100
Lot yield (%) = 100 − Lot defect rate
Use this when lots are your acceptance unit.
Defects and weighted scoring
Total defects = Critical + Major + Minor
DPM = (Total defects ÷ Units inspected) × 1,000,000
Weighted defect rate (%) = (Critical×Wc + Major×Wm + Minor×Wn) ÷ Units inspected × 100
How to use this calculator
- Enter total units received and units inspected.
- Add scrap and rework units from inspection results.
- Decide whether rework counts as a defect.
- Optionally enter lots received and defective lots.
- Record defect counts by severity for deeper insights.
- Adjust severity weights to match business impact.
- Press Calculate and download CSV or PDF reports.
Incoming quality baselines for supplier scorecards
Start with consistent incoming inspection data per supplier and period. Record units received, units inspected, scrap, and rework. When inspection is sampled, the inspected quantity becomes the denominator, so keep one sampling plan. Track shifts after corrective actions or process changes. A weekly or monthly cadence supports trends and supplier reviews. For screening, compare defect rate and PPM to the prior periods.
Unit defect rate and yield interpretation
Unit defect rate is defective units divided by inspected units, expressed as a percentage. If you include rework, the rate reflects total quality burden, not just rejects. Yield is 100 minus the defect rate, showing the share of accepted units. Example: 20 defective units out of 1,000 inspected equals 2.000% and 98.000% yield. In many operations, moving from 1.5% to 0.8% is meaningful.
PPM and DPM for benchmarking across volume
PPM converts defect rate into a comparable scale: defective units per million inspected. A 1.0% defect rate equals 10,000 PPM, while 0.25% equals 2,500 PPM. DPM uses total defects found, not defective units, which helps when one unit has multiple defects. Use PPM for supplier comparisons and DPM for process analysis. Keep definitions consistent, especially whether cosmetic issues count.
Lot performance and acceptance risk
Lots received and defective lots provide a delivery-level view. Lot defect rate is defective lots divided by lots received, and lot yield is 100 minus that rate. This helps when a failed lot triggers sorting, rework, or expedited replacements. A supplier can show low unit defect rate but high lot failure, pointing to packaging, labeling, or mixed-material issues. Review failed lots for repeat causes and containment.
Weighted severity scoring to prioritize action
Not all defects carry the same risk. Weighted scoring multiplies critical, major, and minor defects by severity weights, then normalizes by inspected units. Set weights to reflect safety, compliance, warranty, or rework cost. For example, critical weight 5 and major weight 3 emphasizes high-risk failures. Use the weighted rate to rank suppliers when volumes differ. Combine the rating with on-time delivery and responsiveness for a balanced view.
FAQs
What is the supplier defect rate?
It is the percentage of defective units found during inspection, calculated from defective units divided by units inspected. Defective units can include scrap only, or scrap plus rework, depending on your policy.
Should I use total received or inspected units?
Use inspected units as the denominator, especially when sampling. If you inspect everything, inspected equals received. Keep the inspection basis consistent across suppliers and periods to avoid misleading comparisons.
How do PPM and DPM differ?
PPM is defective units per million inspected units. DPM is total defects per million inspected units, useful when one unit can contain multiple defects. Choose one standard and document your defect counting rules.
Why track lot defect rate?
Lot metrics show delivery-level risk. A single failed lot may cause sorting, downtime, or urgent replacements even if unit defect rate looks acceptable. Track defective lots to spot packaging, labeling, or mix issues.
How should I set severity weights?
Set weights to reflect business impact. Critical defects usually carry higher weights because of safety, compliance, or warranty risk. Keep weights stable for trend analysis, and adjust only when your impact model changes.
Can I export results for audits?
Yes. After calculating, download a CSV for spreadsheets or a PDF summary for sharing and audit files. The exports reflect the latest calculation stored for your session.