Enter tolerance and process inputs
Use nominal deviations or direct limits. The form supports asymmetric zones, guard bands, and optional capability analysis.
Example data table
This sample inspection table shows how measured dimensions relate to the same tolerance zone and acceptance window.
| Part ID | Nominal | LSL | USL | Measured | Deviation | Status |
|---|---|---|---|---|---|---|
| A-101 | 50.000 | 49.850 | 50.250 | 50.040 | 0.040 | Pass |
| A-102 | 50.000 | 49.850 | 50.250 | 49.910 | -0.090 | Pass |
| A-103 | 50.000 | 49.850 | 50.250 | 50.210 | 0.210 | Pass |
| A-104 | 50.000 | 49.850 | 50.250 | 49.840 | -0.160 | Fail |
| A-105 | 50.000 | 49.850 | 50.250 | 50.255 | 0.255 | Fail |
Formula used
Specification limits from nominal mode:
USL = Nominal + Upper Deviation
LSL = Nominal + Lower Deviation
Total tolerance zone:
Zone Width = USL - LSL
Zone midpoint:
Midpoint = (USL + LSL) / 2
Measured deviation:
Deviation = Actual - Nominal
Acceptance limits with protection:
Upper Acceptance = USL - Guard Band - Uncertainty
Lower Acceptance = LSL + Guard Band + Uncertainty
Process capability:
Cp = (USL - LSL) / (6 × Sigma)
Cpk = min((USL - Mean)/(3 × Sigma), (Mean - LSL)/(3 × Sigma))
Percent tolerance used:
|Actual - Nominal| / Side Tolerance × 100
These equations help quantify fit, centering, inspection risk, and process capability for quality review, setup approval, and tolerance monitoring.
How to use this calculator
- Select the input mode based on how your specification is documented.
- Enter the nominal target and deviations, or directly enter LSL and USL.
- Add the measured value for the inspected part or sample.
- Optionally enter process mean, sigma, guard band, and measurement uncertainty.
- Submit the form to view specification status, acceptance result, margins, and capability indicators.
- Download the result as CSV or PDF for traceability and reporting.
Frequently asked questions
1. What is a tolerance zone?
A tolerance zone is the full acceptable range between the lower and upper specification limits. Any measured value inside that range meets the dimensional requirement, subject to your acceptance policy.
2. Why are guard bands useful?
Guard bands shrink the acceptance window to reduce false accept decisions. They are helpful when measurement uncertainty exists and you need extra protection near the specification boundaries.
3. What does tolerance used mean?
Tolerance used shows how much of the available side tolerance the current measurement consumes. A higher percentage means the value is closer to the relevant specification limit.
4. When should I use direct limits mode?
Use direct limits mode when drawings, control plans, or customer specifications already list LSL and USL. This avoids converting from nominal and deviations manually.
5. What is the difference between Cp and Cpk?
Cp measures potential capability using total spread only. Cpk also considers how centered the process mean is within the tolerance zone, making it more realistic.
6. Can this calculator handle asymmetric tolerances?
Yes. You can enter different upper and lower deviations around the nominal target. The tool then builds the correct asymmetric zone and evaluates the measured value against it.
7. What does estimated out-of-spec rate mean?
It is the predicted defective rate in parts per million, based on an assumed normal distribution using the process mean and sigma values you entered.
8. Should I enter one measurement or a process mean?
Enter the actual measurement to judge a single part. Add process mean and sigma when you also want process capability and defect-rate estimates for ongoing production.