Specification interval
Permitted process or product region around nominal.
Unit Converters
Flow Rate Tolerance Calculator
For commissioning, calibration review, and process acceptance, compare an unrounded measured flow with asymmetric specification and gU-guarded acceptance limits. The measured ±U interval remains visible as evidence but is not applied as a second hidden guard; the page distinguishes Accept, Reject, and Review under the declared rule.
Decision—
Deviation from nominal—
Lower specification—
Upper specification—
Lower acceptance—
Upper acceptance—
Calculation ledgerUnrounded values drive all decisions
| Boundary | Value with unit | Meaning |
|---|
How to use
Apply an explicit guard-band decision rule to one flow result
This page distinguishes product or process specifications from the narrower interval used for acceptance. Enter uncertainty as an absolute expanded half-width and use only the guard rule approved by the governing specification or quality system.
- Confirm nominal flow and asymmetric tolerances come from the current specification.
- Enter the corrected measured flow in the same unit as nominal.
- Enter expanded uncertainty as an absolute half-width, not a percentage or correction.
- Apply the documented guard multiplier without changing it to force a verdict.
- Archive the unrounded measurement, specification, acceptance intervals, and final Review/Accept/Reject result.
Conformity-decision fundamentals
Measurement interval
Corrected result plus and minus expanded uncertainty, retained as evidence.
Guard band
Inward shift gU applied to control false-acceptance risk.
Acceptance interval
Region in which the unrounded measured point must lie under this declared rule.
Review outcome
Point inside specification but outside guarded acceptance.
Result interpretation
Apply the declared point-value guard rule once
Accept means the unrounded measured value lies inside the acceptance limits formed by moving each specification limit inward by gU. Reject means the measured value lies outside specification; values between specification and acceptance remain Review. The displayed measured ±U interval documents uncertainty but is not added to the gU guard a second time.
Decision method
Build specification and acceptance limits before evaluating measurement evidence
Asymmetric limits are calculated independently from nominal. The guard width is gU, acceptance limits move inward by that amount, and the measurement interval is measured ± U.
Decision risk
A wider guard reduces false acceptance but increases inconclusive reviews.
Uncertainty ownership
A manufacturer accuracy limit is not automatically an expanded uncertainty value.
One-sided requirements
Minimum-service or maximum-capacity rules may need a dedicated one-sided decision model.
Decision risk
Choose guard width before seeing the result
The governing procedure should state the rule, coverage convention, and treatment of boundary equality in advance.
Uncertainty basis
Enter an expanded interval, not catalog accuracy
Resolution, calibration, repeatability, installation, and fluid-condition effects require an uncertainty budget before entering U.
One-sided service
Use a dedicated model for minimum-only or maximum-only limits
Cooling-flow minimum and equipment-capacity maximum have different risk directions.
Boundary equality
Document whether touching a limit is acceptable
The implemented rule uses unrounded values; contractual equality conventions still require confirmation.
Process inference
Do not turn one result into process capability
Capability needs a stable distribution, sampling plan, and sufficient observations; this page evaluates one result.
Visual explanation
Read specification, guarded point acceptance, and uncertainty separately
The outer corridor is specification, the inner corridor is the gU-guarded point-value acceptance region, the red marker is the value that controls this declared rule, and the blue segment preserves measured ±U as uncertainty evidence. The segment helps review measurement quality but does not create an additional hidden guard.
Detailed calculation process
LSL = Qn(1 − tL); USL = Qn(1 + tU); AL = LSL + gU; AU = USL − gU; Accept when AL ≤ Qm ≤ AU; Reject when Qm < LSL or Qm > USL
| Symbol | Meaning | Unit |
|---|---|---|
| Qn | nominal flow | selected flow unit |
| tL, tU | lower and upper tolerance fractions | dimensionless |
| U | expanded uncertainty used to form the guard width | selected flow unit |
| g | approved guard multiplier | dimensionless |
| AL, AU | guarded point-value acceptance limits | selected flow unit |
Unrounded decision check:
Default input and assumption register
Freeze the conformity rule before evaluating the measurement
The defaults illustrate a two-sided asymmetric specification with an absolute expanded uncertainty and an inward guard band.
| Input | Default | Decision role | Evidence |
|---|---|---|---|
| Nominal | 100 L/min | specification center | current requirement |
| Measured | 101 L/min | corrected result | test record |
| Tolerance | −5% / +8% | asymmetric limits | specification revision |
| Expanded uncertainty | 1 L/min | measurement half-width | uncertainty report |
| Guard multiplier | 1 | inward acceptance shift | approved rule |
Secondary decision analysis
Distinguish specification, guarded point acceptance, and uncertainty evidence
The live register exposes specification limits, gU-guarded point limits, the unrounded measured value, and measured ±U as a separate evidence interval. This prevents display rounding from changing the declared point-value rule without silently applying uncertainty twice.
| Interval or margin | Lower | Upper | Decision use |
|---|
Source evidence
Retain the complete conformity record
Keep the specification revision, nominal definition, corrected indication, unit, calibration corrections, uncertainty budget, coverage statement, guard-band rule, equality convention, environmental conditions, operator, and timestamp. The reported verdict should remain reproducible after display rounding and after the original instrument is unavailable.
Limitations and consequences
Do not use this interval screen as process capability
The model assumes symmetric expanded uncertainty around one result and does not estimate producer risk, consumer risk, probability of conformance, process stability, sampling uncertainty, or long-run capability. One-sided minimum or maximum requirements require a direction-specific decision model rather than artificial symmetric limits.
Flow-conformity glossary
LSLLower specification limit.
USLUpper specification limit.
Guard bandDistance between specification and acceptance.
Expanded uncertaintyDeclared coverage interval half-width.
False acceptanceAccepting an item that is actually nonconforming.
ReviewEvidence does not support a decisive outcome.
Additional conformity terminology
Decision ruleDocumented procedure linking measurement evidence and uncertainty to Accept, Review, or Reject.
Probability of conformanceModel-based probability that the measurand lies within specification; not calculated by this interval rule.
Practical conformity cases
Pump acceptance test
The point value lies inside specification but outside the gU-guarded acceptance limit, so the declared rule returns Review rather than Accept.
Minimum cooling flow
The unrounded measured value lies below the lower specification and supports Reject despite favorable display rounding.
Use the governing decision rule
This calculator makes the entered rule visible; it does not choose the legal, contractual, or laboratory rule for you.
Flow tolerance FAQ
Why is an in-limit point not always accepted?
The approved gU guard moves acceptance limits inward; a value between specification and acceptance is Review.
What does guard factor zero do?
Acceptance limits coincide with specification limits.
Can the tolerances be asymmetric?
Yes; lower and upper limits are calculated separately.
Is uncertainty a correction?
No. Apply known corrections first; uncertainty describes remaining doubt.
Does the calculator add U twice?
No. U forms the entered gU guard; measured ±U remains visible as evidence and is not applied as a second acceptance contraction.
Does Accept prove process capability?
No. It evaluates one measurement result under one declared rule.
Can I enter percent uncertainty?
Convert it to an absolute half-width first.
Why is Review retained?
It prevents unsupported pass or fail claims at guarded boundaries.
Can this evaluate a one-sided limit?
Use a dedicated one-sided decision model.
Advanced flow tolerance questions
Why should the guard rule be selected before testing?
Selecting the rule after seeing a result permits outcome-driven adjustment. Freeze g, U, specification revision, boundary inclusivity, and the authority approving the rule before evaluation so a later reviewer can reproduce the same disposition from the same evidence.
Can manufacturer accuracy be entered as expanded uncertainty?
Not automatically. Accuracy may be a maximum error, typical performance, or composite claim with an unstated distribution. Obtain a valid uncertainty statement that identifies coverage basis, unit, calibration state, operating condition, and any corrections before using U to form the guard.
Why is Review preferable to forcing Pass or Fail?
Review preserves measured points that remain inside specification but fall outside gU-guarded acceptance. It prevents unsupported conformity claims and routes the evidence to retesting, improved measurement, or the authorized disposition process without pretending that arithmetic alone resolves decision risk.
Why retain measured ±U if the point controls the rule?
The interval communicates the reported measurement coverage, supports metrology review, and remains part of the audit record. The declared acceptance rule still compares the unrounded point once with gU-guarded limits, so the same uncertainty is not silently counted twice.
How should a minimum-flow requirement be evaluated?
Use a dedicated one-sided rule that protects the correct risk direction and defines its own acceptance boundary. Repurposing this symmetric screen by ignoring the upper result can obscure the governing minimum-service requirement and misstate which uncertainty risk is being controlled.
Does Accept mean the underlying process is capable?
No. Accept evaluates one reported point under one declared conformity rule. Process capability requires a stable process, representative sampling, sufficient observations, distribution assessment, and specification performance over time; it cannot be established from one guarded measurement.