Garment Size Grading Rules

Grading is how a single sample size becomes a full size run: each point of measure (POM) steps up or down by a set amount for every size. The tempting shortcut, "add 4 cm of chest per size and you are done," is wrong, and knowing why it is wrong is what separates a production-ready spec sheet from a rejected one.

The one distinction that changes everything: body vs finished garment

The major sizing standards do not publish universal finished-garment grade rules. They describe the human body, and leave the garment to the designer:

• ISO 8559-2:2025 designates clothing sizes from body measurements.
• ISO 8559-3:2018 gives a method for building body-measurement tables and intervals, and explicitly states garment dimensions are out of scope.
• ISO 18890:2018 standardises how to measure a finished garment (POM naming and method), but not how much each POM should grow between sizes.
• BS EN 13402-3:2017 (UK/EU) and ASTM D5585-21 (US women) / ASTM D6240-24a (US men) are likewise body baselines, to be combined with ease, fabric, styling and fit.

So a body interval of +4 cm bust is a fact about people, not a rule for a blazer, a relaxed tee, a puffer and a stretch bodysuit, which all convert that body change into different finished measurements because their ease and fit architecture differ. A single grade applied to every category and every POM overstates what the evidence supports.