Rounding a result with its uncertainty
Report useful digits without treating extra digits as proof of accuracy.
Key knowledge
Retain guard digits during uncertainty calculations, then report the estimate and uncertainty with consistent decimal places. The GUM usually recommends at most two significant digits for standard or expanded uncertainty, with more digits when needed to avoid consequential rounding error. For example, y=12.34567 m with u(y)=0.023 m can be reported as y=12.346 m and u(y)=0.023 m.
Values and equations
y=12.34567 m, u(y)=0.023 m → reported y=12.346 m, u(y)=0.023 m
- y
- Measured estimate in the worked rounding example m
- u(y)
- Standard uncertainty of that estimate m
Conditions and scope
- The example reports a standard uncertainty, not a confidence interval or guaranteed error bound.
- The two-digit rule is guidance rather than a universal requirement; preserve justified extra digits for subsequent calculations or applicable reporting rules.
- A reported digit count alone does not establish accuracy, calibration or traceability.
Sources · 3
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Reported estimates are rounded consistently with stated uncertainty while retaining calculation guard digits to avoid round-off error.
2026-10-10 · Independent Chemistry, Biology and Earth/Cosmos editor (AI editorial review). Source checks and independent AI editorial review of compact reference claims, equations, units, conditions and conceptual mappings. This is not human specialist certification, laboratory accreditation, whole-book verification, or a claim that all possible foundational knowledge is present.
Foundational review
2026-10-10 · Independent AI editorial inspection of this new compact reference entry, its equations, applicability, sources and knowledge connections.
Sources from other places
Scope or convention differs
Guard digits and final rounding avoid false precision; estimate decimal places should reflect the stated uncertainty.
The beginner guide always rounds uncertainty upward; the repository keeps this as a contextual choice and distinguishes standard uncertainty from a coverage interval.
National Physical Laboratory2 sources
- A Beginner’s Guide to Uncertainty of Measurement · GPG11, Issue2 United KingdomEnglishShared standard
13.4 Rounding, pp26–27
- Uncertainty Evaluation · NPL Report MS6 United KingdomEnglishShared standard
Chapter8 validation, meaningful digits and Example22, p97
- A Beginner’s Guide to Uncertainty of Measurement · GPG11, Issue2
Entry details
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- foundation-measurement-reporting-digits
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- foundations-audit.1
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