Apparel size systems: why a size label is not a specification

Buyers ask which size chart we manufacture to, and the honest answer is that we manufacture to theirs, once it says enough to be manufacturable. A great many charts do not. They give a letter or a number and a chest measurement, and leave open whether that chest is the wearer's body or the finished garment, how it was measured, what the other sizes do, and how much deviation is acceptable.

This section is about closing that gap. It sits above the mechanics: how a pattern changes across sizes is covered in pattern making and grading, and whether a garment fits as intended is covered in fit development. What follows is the system those two operate inside.

A label names a size. It does not define one

A size letter is a name for a set of measurements somebody has chosen. Until those measurements exist, the name has no content a factory can act on.

Two brands can both call a garment M and mean different products, because each has decided independently what M refers to. Neither is wrong. There is no external authority that fixes the meaning of M, which is why a factory receiving only a letter has been given a label rather than an instruction.

The same is true of numeric labels. EU 40, UK 12 and US 8 are nomenclatures, and a brand assigns them to its own measurements. That is the reason a cross-market conversion table cannot do the work buyers hope it will, which is the subject of international size conversion.

The standards designate by body, not by garment

There are international and European standards for size designation, and understanding what they actually do clears up more confusion than reading them cover to cover would.

The common thread is the important one. Both systems designate sizes using body dimensions in centimetres, not finished garment measurements. Under ISO 8559-2 the primary dimensions are the body measures used to designate size for consumers, with secondary dimensions available as additional body measures. A designation tells a shopper which body the garment is intended for; it does not tell a factory how large to cut anything.

That single fact is why the distinction between body and garment measurements is the foundation of everything else here.

Nor does a standard describe what retailers actually do. Commercial sizing is a separate layer, and brands generally maintain their own charts developed around their own customer and their own fit. Standards and market practice are two different things, and conflating them produces expectations a supplier cannot meet.

Alpha and numeric labels have the same problem

Alpha sizing, the XS to XXL family, is a set of nominal designations. So is numeric sizing. Neither carries an inherent measurement, and neither is more rigorous than the other; they differ in how many increments they conventionally offer and in what customers in a category expect to see.

Dual designations such as S/M or 40/42 are a third option, covering a wider interval with one size. They increase the proportion of a population a given piece will suit and reduce how precisely it suits any individual within it, which is a legitimate trade for some products and a poor one for others.

Whichever is used, the label is a decision about how to present the range to a customer. It comes at the end of the process rather than the start.

Each step depends on the one before it. Relabelling at the end changes what a customer sees and nothing about the garment.

Deciding the range itself

How many sizes to offer, and which, is a commercial decision with a technical consequence. A size system is built to cover a target population distribution, which is what ISO 8559-3's population groups and ISO 8559-4's coverage ratios formalise: you are choosing how much of your intended customer base a range reaches, and how closely it fits the people within it.

That framing explains something buyers often find puzzling. Two brands can each have internally consistent, well-developed size systems and still offer visibly different ranges, because they targeted different populations and made different coverage choices. Neither has made an error.

Extended ranges deserve a note of caution. Continuing a single grade rule outwards indefinitely assumes that bodies scale uniformly, and beyond a certain point proportions change rather than simply enlarging. Where a range extends substantially, the grading may need reviewing rather than continuing, which is a pattern question best raised with the grading reference in view.

Unisex is not a measurement system

Describing a range as unisex says who it is offered to, not what it measures. The garment still needs a target body basis, a base size, finished measurements and grading rules, and someone still has to decide what those are.

In practice a unisex range is a set of proportions chosen to work acceptably across a broader group than a range developed for one. That usually means a straighter body, wider intervals and a fit intent with more tolerance built in. It is a design strategy with measurable consequences, not a shortcut around defining them.

The same applies to ranges developed for a particular wearer group: the target body dimensions, the proportions, the base size and the intervals may all differ, and those differences come from measurement data and fit strategy rather than from assumption.

Grading, conversion and tolerance are three things

These get used interchangeably in enquiries and they are not interchangeable at all.

The distinction between the first and the third often catches people out. A four-centimetre step between sizes is intended. A tolerance is the band either side of each target within which a garment still conforms. Confusing them produces specifications where the tolerance is wide enough to blur adjacent sizes into each other, which no amount of careful sewing can rescue.

What to send

How to turn that into a working document, including the path when a buyer has no chart at all, is covered in building a size chart for production.

Where Voyager fits

For production the reliable starting point is an approved measurement specification rather than a nominal size label. Where a buyer has a chart, we work to it and raise anything ambiguous before sampling. Where a buyer has a reference garment instead, it can be measured and used as the basis for a specification, with the limits of that approach set out in manufacturing from a reference garment. Fit is confirmed on samples before bulk.