What is guard banding in ISO 17025?

Guard banding adjusts acceptance limits inward from specification limits to reduce false acceptance risk when measurement uncertainty is significant.

How should I choose a decision rule?

Choose a rule based on customer requirements, risk appetite, and accreditation expectations. Document the selected rule and apply it consistently.

Does this calculator replace lab procedures?

No. It is a planning aid. Final conformity statements must follow your controlled procedures and approved uncertainty models.

Free Tool

Guard banding decision rule calculator

Estimate guard-banded acceptance limits from your specification and uncertainty inputs. Use the generated decision table as a practical aid for ISO 17025 conformity workflows.

Decision inputs

Set spec limits, uncertainty, and guard band strategy.

Acceptance limits

Results update instantly as inputs change.

Lower acceptance

Upper acceptance

Guard band width

Measured result zone	Decision outcome	Conformity statement hint

Decision support only. Apply your approved lab decision rule and reporting language before issuing certificates.

How to interpret guard banding output

Guard banding narrows the acceptance zone to reduce false accept risk. Larger guard bands increase rejection protection but also increase false reject probability.

Document the decision rule in contracts or quality procedures.
Keep uncertainty evidence traceable to current method validation.
Review guard band assumptions when uncertainty changes.

Guard banding FAQ

What if acceptance limits overlap? If guard band is too large for the tolerance width, there is no practical pass region.

Should all tests use guard banding? Not always. Use where uncertainty is meaningful relative to tolerance and risk requires tighter control.

Can I show this in audit records? Yes, as supporting rationale if your formal decision rule is documented and approved.

Need decision rules tied to live calibration events?

Manage calibration timelines, failed events, and audit-ready history with reminders and attachment tracking.

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