Measurement Uncertainty Budget Calculator

How the measurement uncertainty budget calculator works

Multiply each standard uncertainty by its sensitivity coefficient to express contributions in one output unit. Combined variance sums their squares plus twice the correlation coefficient times weighted components 1 and 2. Component 3 is independent.

The square root is combined standard uncertainty; multiply by the entered k for expanded uncertainty. Inputs are standard uncertainties, not unexplained expanded bounds, and coefficients may be signed.

A qualified measurement model must justify distributions, linearization, dependencies and k. No effective degrees of freedom or confidence level is determined; k = 2 alone does not guarantee 95% coverage. This small first-order budget is not calibration certification.

Worked example

With standard uncertainties 0.3 and 0.4, unit sensitivities, an independent zero third contribution and zero correlation, combined uncertainty is sqrt(0.09 + 0.16) = 0.5. At k = 2, expanded uncertainty is 1.0. Correlation +1 makes it 1.4.

Sources and assumptions

The source material explains the underlying calculation or pricing structure. Entered prices, costs, schedules and scenario choices are your assumptions; this tool does not obtain supplier quotes or predict actual results.

• NIST TN 1297: combined standard uncertainty and covariance