p Chart Limits
Calculate varying-sample-size limits for the proportion of defective units.
p Chart Limits
Browser-only calculations · No input data saved
Worked example results
- Weighted p-bar
- 0.06
| Sample | Defectives | Inspected | p | LCL | UCL | Signal |
|---|---|---|---|---|---|---|
| 1 | 5 | 100 | 0.05 | 0 | 0.131246 | Within limits |
| 2 | 8 | 100 | 0.08 | 0 | 0.131246 | Within limits |
| 3 | 4 | 80 | 0.05 | 0 | 0.139656 | Within limits |
| 4 | 7 | 120 | 0.058333 | 0 | 0.125038 | Within limits |
Rounded for display only. Export includes the inputs, results, method and assumptions. Refreshing or leaving the tool clears entered data.
How to use p Chart Limits
- Load the worked example to see the required input format.
- Calculate varying-sample-size limits for the proportion of defective units. Use consistent units, periods and definitions.
- Select Calculate, review the assumptions and export the result for your project evidence.
Formula and method
p-bar = total defective units / total inspected; limits for sample n are p-bar ± 3√(p-bar(1−p-bar)/n), clipped to [0,1].
Interpretation and assumptions
Count defective units, not total defects. Assumes independent binomial outcomes with a stable underlying probability. Small expected counts need exact binomial limits. Overdispersion may require a different chart.
Results support professional judgement. They are not a certification of process stability, a financial commitment or a substitute for study design.
Frequently asked questions
How do I use the p chart limits?
Calculate varying-sample-size limits for the proportion of defective units. Load the example first, then replace all inputs with consistent process data and select Calculate. p-bar = total defective units / total inspected; limits for sample n are p-bar ± 3√(p-bar(1−p-bar)/n), clipped to [0,1].
What assumptions matter for p chart limits?
Count defective units, not total defects. Assumes independent binomial outcomes with a stable underlying probability. Small expected counts need exact binomial limits. Overdispersion may require a different chart.
Are my calculator inputs saved or sent to a server?
These native calculations run in this browser tab. Inputs are not sent to a server or saved by this calculator. Download the result if you need a record; leaving or refreshing clears the form.