Measurement Uncertainty Calculator
Estimate combined and expanded uncertainty for laboratory measurements following ISO GUM and ISO 15189:2022 principles.
Core Lab Tools provide rapid calculations and can be extended into full Clinical Intelligence Systems.
Input & Computation
ISO 15189:2022 requires laboratories to determine measurement uncertainty for every quantitative examination. The expanded uncertainty U at k=2 represents the interval within which the true value lies with ~95% confidence — a concept patients and clinicians increasingly expect to see alongside results.
Enter Uncertainty Components
Use the same units for all inputs. Type A from repeated measurements; Type B from calibration or systematic sources.
Imprecision from repeated measurements — SD from IQC or method validation
Systematic uncertainty from calibration, bias, or reference material — in same units as Type A
k=2 → ~95% confidence (default)
To express result as x ± U
Interpretation Guide
ISO GUM Formulas
Uc = √(uA² + uB²)
U = k × Uc
Result = x ± U
Coverage Factor k
- k = 1— ~68% confidence
- k = 2— ~95% confidence (standard)
- k = 3— ~99.7% confidence
Evidence & References
JCGM 100:2008 — ISO GUM
Evaluation of measurement data — Guide to the Expression of Uncertainty in Measurement. Joint Committee for Guides in Metrology. The foundational document for all uncertainty calculations.
ISO 15189:2022
Medical laboratories — Requirements for quality and competence. Clause 7.3.7 explicitly requires reporting of measurement uncertainty for quantitative examinations.
ISO/IEC 17025:2017
General requirements for the competence of testing and calibration laboratories. Section 7.6: Evaluation of measurement uncertainty.
EURACHEM/CITAC CG 4 (2012)
Quantifying Uncertainty in Analytical Measurement. 3rd edition. European analytical chemistry guidance applying GUM to chemical measurements.
CLSI EP29-A (2012)
Expression of Measurement Uncertainty in Laboratory Medicine. Approved Guideline. Wayne, PA: CLSI.
This tool implements the Type A + Type B quadrature combination model (ISO GUM Clause 4). The model assumes uncorrelated uncertainty sources and normal distribution for the expanded uncertainty calculation.
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When to Use
- Method validation documentation for new or modified analytical methods
- NABL / ISO 15189:2022 and ISO/IEC 17025:2017 accreditation audits
- Reporting expanded uncertainty (U) alongside patient or reference results
- High-precision assays where measurement reliability is critical
- Evaluating and comparing uncertainty across different measurement systems
Common Pitfalls
- Ignoring systematic bias — Type B uncertainty is often underestimated or omitted entirely
- Using incorrect coverage factor — k=2 applies only for normal distributions at ~95% confidence
- Underestimating uncertainty sources — pre-analytical factors (sampling, stability) contribute but are often excluded
- Not reporting uncertainty in critical tests — ISO 15189 requires U to accompany quantitative results
- Confusing combined uncertainty u(c) with expanded U — always report U = k × u(c) to clinicians