Helmet Head Measurement Guide

Convert head circumference only; confirm fit with the exact model chart.

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Helmet head-measurement guide

Measurement anchored Reference review · July 2026

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Category	Reference basis	Used for	Last review
Shoes	ISO 9407:2019 ISO 19407:2023	Mondopoint and footwear-system methodology	July 2026
Rings	ISO 8653:2016	Ring-size designation	July 2026
Helmets	U.S. CPSC fit guidance	Fit and safety guidance only	July 2026
Clothing, belts, hats and gloves	Measurement anchors with conservative confidence labels	General comparison; exact brand charts remain controlling	July 2026

No brand endorsement is implied. Product-specific charts can override a general conversion.

Only audited calculations and measurement guidance are active in dataset 5.4.0.