Every brand drafts to its own fit model, so identical labels rarely mean identical garments.
Fit models and blocks
Brands develop patterns around a fit model with specific proportions, then grade sizes up and down from that base block. Two brands with different fit models will produce different garments under the same label.
Grading rules differ
Grading decides how much each measurement grows per size step. A brand that adds four centimetres to the bust per step and another that adds five will diverge quickly at the extremes of the range.
Target market and vanity sizing
Labels are also a marketing decision. Some retailers deliberately assign smaller numbers to larger garments, which is why older wardrobe items are a poor reference point.
What to do about it
Treat converters as a starting point, then verify against the specific product's measurement chart. Reading recent customer feedback about whether an item runs small or large is often the fastest correction available.
Frequently Asked Questions
Are size charts on retailer sites reliable?
Product-level measurement charts are the most reliable source available. Generic brand-wide charts are less precise.
Why does the same brand fit differently across lines?
Separate product lines often use separate blocks, particularly for sports versus casual ranges.