Two garments, same label, same brand, same season. One came off a rail in a shop and fits through the shoulder. The other arrived in a polybag, ordered in the identical size from the same website, and binds across the upper back while hanging loose at the waist. Nothing has gone wrong in the warehouse. The two dresses were almost certainly developed from different blocks, by different teams, on different timelines, and the size label on each is a claim about a different body.

This is the part of extended sizing that retailers discuss internally and almost never in public. The in-store range and the online-exclusive range are frequently not one continuous size run. They are two products that share a name.

A size label is the output of a block, not a measurement of you

Every commercial garment starts from a block: a master pattern built to one set of body measurements, called the base size or sample size. The pattern cutter develops the style on that block. Everything above and below it is produced by grading — adding or subtracting increments at defined points on the pattern so the shape scales up and down. The increments are set by a grade rule, and the grade rule is a house decision. It is not physics.

Where the trouble sits is in the choice of base size and the distance the grade has to travel. Grading works cleanly close to the base and starts to distort at range. Circumferences scale predictably. Lengths, depths and curves do not. The armhole, the scye, is the usual casualty: add girth to a bodice by grading outward and the armhole grows in circumference along with it, which is why a size run pushed a long way up its own grade produces a sleeve opening you could fit a forearm through and a bicep that still won't close. Neck drop, shoulder slope, bust apex placement, the rise on a trouser, the depth of a crotch curve — these need to be re-plotted, not scaled.

A well-graded extended range therefore isn't the small range with more added. It is developed on its own block, with its own base size somewhere inside the extended run, and fitted on a fit model whose measurements sit in that range. That is more pattern work, more sampling, more fitting, more time. It is also the single thing most likely to be skipped.

Online-exclusive ranges are built under different constraints

When a retailer extends sizing online only, the decision is usually commercial before it is technical. Shop floors are finite and merchandised to expected sell-through per square metre. A web page is not. Extended sizes go online because online carries the inventory risk differently — and because the order can be routed to a different supplier, on a different lead time, with a different technical pack.

That last part is the mechanism. Sizing lives in the technical pack: the spec sheet, the measurement points, the grade rules, the tolerances a factory is allowed to work within. If the extended range is sourced from a different factory or developed by a different product team, it can carry a different pack. Same brand, same style name, different rules for how the thing is cut. Nobody has to have decided to make the two ranges inconsistent. It happens by structure.

The observable symptom is a garment that reads as a scaled-up version of a smaller original — long in the body, wide in the armhole, shallow through the bust, with a waist that lands above where your waist is. That is a bodice graded a long way from a base size that sits well below the size printed on the label. The other symptom is the opposite: an extended range developed properly on its own block, so it fits in the shoulder and the bust but does not sit on the same length or waist placement as the in-store version of the same style. Both are the same underlying fact. There are two patterns.

Size charts are the part you can actually audit

The retailer will not tell you which block a garment came from. It will frequently tell you, without meaning to, that two blocks exist. Look for the tell in the published measurements.

  • A separate size guide, tab or page for the extended range rather than one continuous chart running through all sizes. Two charts means two sets of numbers were arrived at separately.
  • A change in the grade interval partway up the chart. Bust and hip stepping at one increment through the lower sizes, then jumping to a larger increment above a certain point, is a grade rule changing mid-run.
  • Body length, back length or inside leg that stops varying, or starts varying, at the point where the extended range begins.
  • Garment measurements offered for one range and body measurements for the other. Those are not comparable figures and cannot be read against each other.
  • Sizes expressed differently across the run — numeric in store, alpha online, or a chart that pairs one numeric size with two alpha equivalents.
  • Style names and product codes that differ between the in-store and online listing of what is presented as the same garment.

None of this proves a separate block on its own. All of it is evidence that the two ranges were specified by different hands, which is the condition under which the same label stops describing the same garment.

What to do with a garment in front of you

Fit the shoulder and the armhole first, because those are what a pattern cutter cannot fake and what an alteration hand can rarely fix cheaply. Put your arm forward. If the scye is cutting at the front, the armhole has been graded wide and shallow rather than re-plotted, and no amount of taking in at the side seam will change it. If the shoulder seam sits out on your upper arm on a set-in sleeve, the garment was graded, not drafted, for the size you are holding.

Then find the waist. On a fitted or semi-fitted bodice, the narrowest point of the garment should sit at the narrowest point of you. If it lands higher, the length was graded from a shorter base size, and that is the clearest single indicator that you are wearing a scaled-up small pattern. It also tells you the range this garment came from will do the same thing in every style, which is useful information about a whole line from one try-on.

Check the seam allowance while you are there. Turn the side seam and the centre back out. An allowance you can pinch — a usable one rather than an overlocked sliver — means a garment that can be let out, and it also signals a maker who expected the piece to be fitted rather than shifted. Volume ranges are often cut with minimal allowance because the shape is meant to skim and nobody costed in alteration.

And keep the receipts, in the literal sense. Ordering the same style in the same size from the shop and from the site, and returning the one that loses, is not indecision. It is the only test available to you, because the retailer publishes one size and sells you two.