Posture is the fitting problem no size chart asks about

A tape measure records size and ignores stance

Every size chart in the world asks for circumferences and lengths: chest, waist, hip, inside leg, sleeve. Those numbers describe how much of you there is. They are silent on the question of how it’s arranged, and arrangement is where a great many fitting complaints actually begin.

Consider two people who measure identically around the chest. One stands with the shoulders rolled slightly forward and the head carried ahead of the spine, which is close to what a working life at a desk produces. The other stands with the chest open and the upper back flat, which is what years of carrying loads or of certain kinds of training tend to produce. The same garment won’t sit the same way on them, and neither of them is doing anything wrong.

A cutter working to measure will look at a client from the side before touching a tape, because the side view carries the information that the front view hides.

Balance is the name for what posture disturbs

The technical term is balance: the relationship between the length of a garment down the front and its length down the back, measured from the shoulder line. A pattern is drafted with a particular balance built into it, and that balance assumes a stance.

When the wearer stands differently from the assumption, cloth has to come from somewhere. A rounded upper back is physically longer over the top than a flat one, so the back of the garment is short and it borrows length from the front by riding up. The visible result is a collar that stands away from the neck, a hem that hangs lower at the front than the back, and drag lines that run from the shoulder blades outwards.

The forward stance takes cloth from the front

The most common variation, at least among people who spend their days at screens, is some degree of forward head carriage with rounding through the upper back and shoulders. It is worth saying plainly that this is a description of a shape, not a diagnosis of anything; posture varies enormously and a great deal of it is simply how a person is built.

On a jacket the signs are consistent. The collar lifts off the neck at the back. The front hem drops and the two front edges swing apart below the button rather than hanging parallel. Sleeves often look slightly long at the front and short at the back, because the arm itself is hanging further forward than the sleeve was cut for.

On a shirt, the same stance produces a back that pulls tight across the shoulder blades whenever the arms come forward, and a front that gathers into soft folds under the collarbones. Shirts are unstructured enough to absorb a certain amount of this. Jackets are not, which is why the fault is far more visible in tailoring.

The upright stance fails the other way round

The opposite build is less common and it produces the mirror image of every symptom. A flat, open upper back is short over the top and long down the front, so the garment has surplus length at the back and not enough at the front.

You see it as horizontal folds pooling above the seat or across the small of the back, a front hem that kicks up rather than dropping, and a jacket that seems to want to slide backwards off the shoulders. People often describe such a garment as too big, and then buy a smaller one, which pulls the front tighter without touching the surplus behind.

What a tailor changes, and the order it happens in

For a garment already made, the standard remedies are limited but real. Length can be added to the back neck area by letting out the seam allowance at the centre back and the collar, or removed by taking it in, and a competent alterations tailor will look there first when a collar gaps. The shoulder seam itself can sometimes be re-set slightly further back or forward, which is expensive work with real risk attached.

A shoulder pad can be adjusted, replaced or removed, and on a soft jacket that can move a surprising amount of cloth. Hems can be levelled once everything above them has settled. What cannot be done afterwards is redrafting the fundamental balance of a pattern, because that decision was made before the cloth was cut.

Looking at yourself from the side

The useful habit in a fitting room is to turn side-on and look, rather than facing forward and assessing width. Stand as you normally stand, not as you stand when you are being looked at, because a corrected posture held for thirty seconds tells you nothing about the garment you will actually wear.

Then check three things: whether the collar touches the neck all the way round, whether the front and back hems finish level, and whether the front edges hang parallel or swing. Those three observations will separate a garment that needs the sleeves shortening from one that will never quite settle. And a poor result is not a verdict on the body: a garment is an object drafted from assumptions, so when the assumptions miss, the honest description is that the pattern does not suit you rather than the reverse.