Fit Blocks, Explained

A fit block is a full CAD pattern — front, back, sleeve, collar, cuff — held at one base size (usually adult unisex M). It captures four things every downstream style inherits:

• Ease — how much space the garment gives past the body measurement at every landmark.
• Balance — where the shoulder point sits, the pitch of the sleeve, how the front and back panels relate.
• Silhouette — how the garment hangs on the body from shoulder to hem.
• Grade rules — how the pattern scales up (M→L→XL) and down (M→S→XS).

Ease is measured as garment circumference minus body circumference at the same landmark. Compression-grade poly-spandex blocks use negative ease — the finished garment is smaller than the body and stretches on.

• Pick a target consumer and their body-measurement centreline (usually adult unisex M chest 96–104 cm).
• Draft the block off the target measurements plus the chosen ease grid.
• Cut a first sample in the intended production fabric — not a substitute — and pressure-test the ease on real bodies.
• Wear-test the block on 3–5 bodies at the base size; adjust shoulder slope, armhole depth and sleeve pitch.
• Grade the signed-off block up and down; the grade rules travel with the block for every future style.

When a factory drafts your block, they own it. When another brand asks the same factory for a "similar fit", they get your block by default. The correct commercial practice is to have blocks drafted specifically for the brand and held under a mutual IP agreement — the pattern files travel with the brand, not the factory.