GIFSQ Tools · Module 15 — Metrology, Validation & Laboratory Accreditation · Tool 282 of 500
Build a measurement uncertainty budget from your standard uncertainty components: combined uncertainty, expanded uncertainty, and the share of the largest contributor — the table every ISO/IEC 17025 uncertainty budget needs.
Try sample values — fills the form with the worked example below.
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Combined uncertainty (uᶜ)
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Expanded uncertainty (U)
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Largest contributor (%)
Equation: uᶜ = √(Σuᵢ²). U = k × uᶜ. Largest contributor (%) = largest uᵢ² ÷ Σuᵢ² × 100.
Method: Uncertainty budget per Eurachem/CITAC Guide CG4 and GUM (JCGM 100): list every component as a standard uncertainty, combine by root-sum-of-squares, and identify the dominant contributor so improvement effort goes to the right place.
Assumptions: the components are independent standard uncertainties in the same unit; each component already includes its own divisor (for example a rectangular distribution divided by √3).
Limitations: a budget is only as good as its component list — a missing source (sampling, preparation, calibration) is not detected by the arithmetic; correlated components need covariance terms.
Rounding: combined and expanded uncertainty to 2 decimal places; largest contributor to 2 decimal places; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: Uncertainty budget per Eurachem/CITAC Guide CG4 and GUM (JCGM 100): list every component as a standard uncertainty, combine by root-sum-of-squares, and identify the dominant contributor so improvement effort goes to the right place.
Assumptions: the components are independent standard uncertainties in the same unit; each component already includes its own divisor (for example a rectangular distribution divided by √3).
Limitations: a budget is only as good as its component list — a missing source (sampling, preparation, calibration) is not detected by the arithmetic; correlated components need covariance terms.
Rounding: combined and expanded uncertainty to 2 decimal places; largest contributor to 2 decimal places; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: Components 0.5, 0.3, 0.4 and 0.2 mg/kg with k = 2: uᶜ = √(0.54) = 0.73 mg/kg, U = 1.47 mg/kg, largest contributor = 0.25 ÷ 0.54 × 100 = 46.30% (the 0.5 mg/kg component).
Enter values above to see results.
If one contributor is above 80%, improving that single source is the fastest way to shrink the budget. Tool 282 of 500 — GIFSQ
