Free Engineering Tool
Measurement Uncertainty Calculator
Calculate combined and expanded measurement uncertainty per GUM / ISO 17025. Enter up to 6 uncertainty sources with Type A or B classification.
Results
Combined Standard Uncertainty
Expanded Uncertainty
Where k = coverage factor (k=2 for ~95% confidence, k=3 for ~99.7%).
Divisors by Distribution
Type A (statistical): divisor = 1 (value is already a standard uncertainty from s/√n).
Type B (Normal, from certificate U at k=2): divisor = 2.
Type B (Rectangular, half-width a): divisor = √3 ≈ 1.732.
Measurement uncertainty quantifies the doubt about a measurement result. It defines a range within which the true value lies with stated probability (typically 95%). Required by ISO 17025 for all labs.
Type A = evaluated by statistical analysis (repeated measurements → standard deviation of mean). Type B = evaluated from other info: calibration certificates, specifications, published data, experience.
k multiplies combined standard uncertainty to give expanded uncertainty. k=2 ≈ 95% confidence. k=3 ≈ 99.7%. k=2 is the default for most calibrations.
For independent sources: RSS (root sum of squares): uc = √(u₁² + u₂² + u₃² + ...). Each source value is first divided by its divisor to get standard uncertainty.
GUM (Guide to the Expression of Uncertainty in Measurement) is the international guide published by JCGM. It is the basis for ISO 17025 uncertainty requirements and provides the framework for evaluating and expressing measurement uncertainty.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Calibrated vibration measurement instruments for traceable, ISO 17025–compliant data.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
