Apparel sizing (Castelli vs Rapha vs PEdALED, wildly inconsistent), how do you handle on Magento?

Cycling apparel sizing is famously inconsistent. Castelli runs Italian-small (US M = Castelli L). Rapha runs Euro-fit (true to body measurements). PEdALED + Maap run modern athletic fit. Returns for size hit 25-35% on cycling apparel.

Magento setup that cuts it to ~15%:

• Per-brand sizing chart attribute, each apparel product has a chest, waist, hip, sleeve measurements table (in cm AND inches). Rendered on PDP as an interactive modal, not a buried PDF.
• “Find your size” calculator, customer enters chest + height + preferred fit (race / endurance), recommends a size with confidence indicator. Built per brand because the math differs.
• Brand comparison widget, if the customer owns a Rapha Pro Team jersey size M and is looking at a Castelli Aero Race jersey, widget shows “you probably want Castelli size L.” Built as a comparison JSON table.
• Customer-submitted “fit feedback”, post-purchase email asks “did this fit?” with a 1-tap response. Aggregated to a per-SKU “runs small / true to size / runs large” flag displayed on PDP.
• Free-return policy on first-time apparel orders, reduces sizing-anxiety friction. Implemented via Returns Magic / Loop Returns integration.

Cost: $5k, $12k for the full sizing stack. ROI is fast, cutting apparel returns from 30% to 15% on a $2M apparel-revenue store recovers $150k+ of inventory + shipping cost per year.