The letters S, M, L, or XL do not correspond to fixed centimeters. Each brand associates these letters with its own sizing chart, which explains why an M purchased from one retailer may correspond to an L elsewhere. To choose the right size, the starting point remains the same: a measuring tape and three measurements taken on the body.
Vanity sizing: why an M today is not the same as an M yesterday
Since the rise of e-commerce, several major brands have expanded the measurements associated with each letter. A report by TrueFit presented at the NRF in January 2024 describes this phenomenon as vanity sizing: retailers discreetly inflate sizes to flatter consumers and reduce return rates.
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In practice, an M purchased in women’s ready-to-wear today corresponds to measurements that are often larger than they were a few years ago. This phenomenon also affects unisex ranges. Relying solely on the letter printed on the label is akin to betting on the brand’s commercial policy, not on one’s own body shape.
To find out what size corresponds to m or l on a given garment, the only reliable method is to compare your actual measurements with the size guide specific to each manufacturer.
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Chest, waist, hip: the three measurements that matter
Before consulting a size guide, you need to have reliable numbers. Three measurements are sufficient for most everyday garments (tops, bottoms, dresses).
- Chest measurement: measuring tape placed horizontally around the widest part of the bust, under the armpits, without tightening. This measurement determines the size of shirts, t-shirts, and jackets.
- Waist measurement: measured at the natural waistline, just above the navel. Reference for pants, skirts, and belts.
- Hip measurement: measuring tape placed on the fullest part of the hips. Determining for pants, skirts, and fitted dresses.
Take these measurements directly on the skin or over a thin undergarment, keeping the measuring tape flat. If the value falls between two sizes on the guide, opt for the larger size: a slightly loose garment fits better than one that pulls.
Bust and torso length: the forgotten measurement
Most size guides limit themselves to the three circumferences. Some brands are starting to incorporate bust length (from the base of the neck to the waist) into their charts, especially for dress shirts and dresses. A longer torso can affect the fit of a garment even if the circumferences match the displayed size. Measuring this length helps anticipate a problem that the simple choice of M or L does not resolve.
M and L correspondence: reading a size chart without mistakes
A size chart lists ranges of measurements expressed in centimeters next to each letter. A common pitfall is to look at only one line (the chest measurement, for example) and ignore the others.
Cross-reference the lines, don’t choose just one
If your chest measurement falls into M but your hip measurement corresponds to an L, the choice depends on the type of garment. For a top, the chest takes precedence. For pants, the hips prevail. For a dress or jumpsuit, take the larger size between the two results.
French sizes (38, 40, 42) do not exactly correspond to international letters S, M, L. A French 40 may be labeled M by one manufacturer and S by another, depending on the origin of the chart used. The ISO 8559 standard, revised and gradually adopted by European manufacturers in recent years, aims to standardize these correspondences. However, it remains little visible to consumers: most sites still display letters without mentioning this standardization.
Men and women: two distinct size charts
The measurements associated with a men’s M and a women’s M differ significantly. A men’s M corresponds to a wider chest measurement and a higher waist measurement than a women’s M. Wearing a garment from the opposite chart without adjusting the size guarantees a fit issue at the shoulders or hips.
Material and cut: two factors that alter actual size
Two t-shirts labeled M in the same store can fit very differently if one is made of rigid cotton and the other of stretch jersey.
A fabric containing elastane allows for a deviation of one to two centimeters in measurements. A fabric without elasticity allows for no deviation: it’s better to take the size above if there is any doubt. Linen, raw denim, or woven wool behave this way.
The cut plays a similar role. A slim-fit garment fits smaller than a straight-cut garment from the same brand, even if the label shows the same letter. Some manufacturers add a mention (“regular,” “oversized,” “fitted”) next to the size. When this indication exists, it modifies the interpretation of the guide as much as the letter itself.
Check the size before buying online: three concrete reflexes
Returns due to size issues represent a significant portion of returns in e-commerce. Three checks reduce the risk of error.
- Consult the size guide specific to the site, not a generic guide found elsewhere. Each brand applies its own ranges.
- Compare with a garment you already own that fits well: measure it flat (chest width, total length) and compare with the dimensions indicated on the product sheet, when available.
- Read customer reviews filtering for the mention “size”: feedback from buyers who specify their measurements and the size ordered is often worth more than an official chart.
A well-chosen garment relies on centimeters, not on a letter. The next time you hesitate between M and L, place the measuring tape on your body, note three numbers, and compare them to the brand’s guide. The letter will follow.