US/UK/EU/AU bra sizing matrix, how do you handle the conversion politics?

This is the single most underestimated complexity in international lingerie DTC. The labels look similar but the conversions are genuinely incompatible:

• US 38D = UK 38D label-wise but the cup-volume is different. US 38D cup-volume ≈ UK 38C ≈ EU 85C ≈ AU 14C.
• Cup naming diverges past D. US: D, DD, DDD/E, F, G, H, I, J, K. UK: D, DD, E, F, FF, G, GG, H, HH, J, JJ, K. Same cup-volume can be called DDD (US) or E (UK) or 80E (EU) depending on system.
• Band sizing in cm vs inches. EU uses cm bands (75, 80, 85, 90, 95). Conversion to US/UK inches is approximate, a 75 EU is “closer to 34 than 32” but not exact.

The architecture I build:

• One canonical SKU per cup-volume, backend uses US convention (e.g. BRA-X-34DD). Warehouse picks one SKU; one inventory count.
• Size-region lookup table, Magento custom table mapping (canonical_sku, store_view) → label. Customer in uk_store_view sees the SKU labelled “34D”; customer in us_store_view sees “34DD”; customer in eu_store_view sees “75D”.
• Size filter / dropdown on category + PDP renders the regional label per store view via a Hyvä component reading the lookup table.
• Returns flow translates back, customer returns “34D” in UK; system maps to the canonical SKU; stock-update + restock fires correctly.

Shopify Markets shares the catalog and forces you to either run separate stores per region (loses customer reviews + analytics) or fudge the labels (confuses customers). Magento handles it natively via store views, this is the #1 reason multi-region lingerie brands choose Magento.