Size Charts Across Brands, Converted
A medium is not a size. It is a brand’s internal code for a set of garment measurements, and every brand owns a different set — which is why the same letter can fit two body types or none. Converted properly, size charts agree with each other almost perfectly. The conversion tool is not a table of letters; it is a tape measure and a few numbers you record once.
Why the letters disagree
The patterns are broad enough to plan around. Value and fast-fashion labels tend to cut generously — a roomier garment reads as better value on the body, and the letter drifts upward over the years. Italian houses tend to cut closer to the body, so their 48 or M reads smaller than the same code at a mass-market chain. Vintage runs smaller than both. None of this is a secret; it is pattern-making culture. The practical consequence: any method built on letters inherits the drift, and any method built on measurements does not.
Read garment dimensions, not body dimensions
Size charts come in two kinds. A body chart tells you what torso the brand assumes will wear the size. A garment chart tells you what the made shirt actually measures across the chest. Garment charts are the usable ones, because your body is already measured and the distance between the two — the ease — is a small, predictable number per garment type.
If a listing gives only a body chart, check whether the piece is cut fitted or relaxed and treat the result as approximate. If it publishes flat garment dimensions, the cross-brand problem is solved before you add anything to a cart. The same discipline applies at the extreme end of sizing: an overcoat’s usable fit is decided by measured length and chest room for layers, as the overcoat measurement guide covers.
Measure your best-fitting piece once
Button the garment, lay it flat on a table, and smooth it without stretching:
- Chest: measure straight across from armpit seam to armpit seam, then double it. A flat chest width of 21.5 inches is a 43-inch garment.
- Shoulders: seam to seam across the back.
- Sleeve: shoulder seam to cuff, along the top of the arm.
- Back length: bottom of the collar seam straight down to the hem.
Record the chest numbers per category — shirt, tee, knit, blazer, coat. Five measurements and you are converted for life.
The ease table
| Garment | Comfortable chest ease over body |
|---|---|
| Woven shirt | 2–3 inches |
| Tee or light knit | 1–3 inches; close-fit knits can run negative |
| Chunky sweater | 3–4 inches; see gauge and ply |
| Blazer | 3–4 inches, cut to sit over a shirt |
| Overcoat | 4–6 inches, to clear a jacket underneath |
Worked example: the new brand’s chart says a size M measures 43 inches across the chest. Your body measures 40. That is 3 inches of ease — correct for a shirt or blazer, too tight for an overcoat, which sends you up a size or to another brand. The same arithmetic in reverse explains why the twelve-piece audit fails on fit before it fails on style: a piece outside its ease range does not get worn, whatever the letter on the tag says. Denim is the one category where raw measurements shift after break-in, so convert from a worn pair — see denim by the ounce.
FAQ
- Which garment should I measure as my reference?
- The piece you reach for most and fit best in that category. A shirt that fits converts you across every shirt chart; a coat that fits does not convert shirts.
- Do I size up in Italian brands?
- Treat it as a rule of thumb, not a law. Italian cuts generally run closer to the body than American fast fashion, but the garment dimensions on the chart settle the question faster than nationality.
- Is vanity sizing getting worse?
- Letters have drifted larger over decades at the value end of the market, which is exactly why garment measurements beat letter codes. Numbers on a chart cannot quietly inflate; a letter can.
