Gauge Resolution and 10:1 Rule Calculator
A caliper that reads to 0.01 mm cannot reliably judge a 0.02 mm tolerance. This calculator applies the common rule of ten, and softer ratios, to tell you whether the gauge you have can discriminate the tolerance you need.
Your numbers
Upper limit of the characteristic.
Lower limit of the characteristic.
Tolerance divided by gauge resolution.
Smallest increment the gauge displays.
Plus or minus accuracy from the calibration certificate.
Your results
The 10:1 and 4:1 figures are rules of thumb, not requirements of every standard. A proper gage R&R or measurement uncertainty study is the way to confirm a gauge is capable. Follow customer and standard requirements first.
Ratio achieved vs gauge resolution
Sweeps Your gauge resolution from 0.001 to 0.02, holding your other inputs fixed.
Attach approved gauges to inspection plans
Optional: we can review how gauge selection and calibration status could link to your ERP inspection characteristics.
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How to use it
Enter the upper and lower limits from the drawing, choose the ratio your procedure requires, and enter the resolution and calibration accuracy of the gauge. The calculator shows the finest resolution you need and the ratios your gauge achieves. A result flagged zero means the gauge fails the rule, so choose a finer instrument or confirm capability with a gage R&R study. The chart shows how the ratio improves as resolution gets finer.
The rule and its origin
The rule of ten, sometimes called the gagemaker's rule, states that the instrument should discriminate to one tenth of the tolerance. Many quality systems relax this to 4:1 or 5:1 when 10:1 is impractical. The accuracy ratio here compares the tolerance to the full plus and minus accuracy band. Example: tolerance 0.02 mm at 10:1 needs 0.002 mm resolution, so a 0.01 mm caliper fails and a 0.001 mm micrometer passes.
- Required resolution = tolerance / ratio
- Resolution ratio = tolerance / gauge resolution
- Accuracy ratio = tolerance / (2 x accuracy)
- Both resolution and accuracy should meet the rule
Common mistakes
Reading the display digits as accuracy: a digital caliper may display 0.01 mm but be accurate only to 0.02 mm. Also, passing the rule does not prove the measurement system is capable. Operator, fixture and part form errors add variation, which is why gage R&R is the final test. Record the selected gauge on the inspection plan so each characteristic always uses an approved instrument.
Frequently Asked Questions
What is the 10 to 1 rule for gauges?
It says the gauge should resolve to at most one tenth of the tolerance. For a 0.05 mm total tolerance, the gauge should resolve to about 0.005 mm or finer.
Is 4 to 1 acceptable?
Some quality systems accept 4:1 when 10:1 is impractical, but it is a weaker standard. Use whatever your customer or standard requires and back it with gage R&R for critical characteristics.
Does resolution equal accuracy?
No. Resolution is the smallest displayed step. Accuracy is how close readings are to the true value. A gauge can show many digits and still be inaccurate, so check the calibration certificate.
What if the tolerance is one sided?
Use the total tolerance zone that matters, for example the distance between the limit and the nominal for a one sided limit, or follow your procedure. Enter the matching limits as USL and LSL.
If gauge choices are stored on drawings and in people's heads, Netray can help attach approved instruments to ERP inspection plan characteristics.
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