Measurement Uncertainty Calculator
This uncertainty-budget calculator combines independent standard uncertainty contributions by root-sum-square and applies a coverage factor. It is a screening worksheet, not an accredited calibration certificate.
Run the calculation
Your data stays in this browser. No measurements are uploaded.
- 1 Enter data
- 2 Review results
- 3 Take action
Ready for your data
Complete the inputs or load the worked example. Results will include the primary decision, interpretation and supporting metrics.
Worked example
Combining calibration 0.002 mm, repeatability 0.0015 mm and resolution 0.0006 mm as standard uncertainties gives uc ≈ 0.00257 mm and U ≈ 0.00514 mm for k = 2.
Load the example in the calculatorFormula and methodology
- Enter every source as a standard uncertainty in the same output unit.
- Multiply each source by its sensitivity coefficient.
- Independent contributions are combined by root-sum-square; expanded uncertainty is k × combined uncertainty.
uc = √Σ(ci × ui)²U = k × ucContribution % = (ciui)² / uc² × 100 How to interpret the result
- Expanded uncertainty needs a stated coverage factor and probability interpretation.
- Correlated inputs, non-linear models and non-normal distributions require additional treatment.
- Conformance decisions may require guard bands and an agreed decision rule.
Common errors and limitations
- Entering expanded uncertainty as if it were standard uncertainty.
- Mixing units or forgetting divisors used for rectangular distributions.
- Assuming k = 2 always provides exactly 95% coverage.
Turn the calculation into an engineering decision
Share the drawing, process conditions and result context. AccuTouch can review the measurement, fixture, SPC or automation starting point.
Frequently asked questions
Type A vs Type B uncertainty?
Type A is evaluated statistically from observations. Type B uses other information such as calibration certificates, resolution or specifications. Both become standard uncertainties before combination.
What coverage factor should I use?
Use the factor required by the applicable method and degrees-of-freedom assessment. k = 2 is common but not universally sufficient.
Does this support correlation?
No. This version assumes independent input quantities.
Technical references
Use the current controlled standard or your organisation’s approved method where it differs from this screening tool.
Method content reviewed 13 August 2026. Independent technical approval is still required before production publication or use in a controlled quality procedure.