Break is the fold that appears where a trouser hem meets the shoe. It is discussed as a style preference, but it is really the visible result of two measurements interacting.
Break is a consequence, not a setting
A trouser hem rests on the shoe. If the leg is longer than the distance to the shoe, the excess has to go somewhere, and it goes into a fold.
The size of that fold is the break. It is produced by hem length, and no separate adjustment controls it.
Which is why a tailor asks where the hem should sit rather than which break the customer wants, since the second follows from the first.
Leg opening changes the same length
A wide leg opening has more fabric circumference to absorb, so a given excess length produces a soft, shallow fold spread across the width.
A narrow opening has less room, so the same excess buckles into a sharper, more visible crease that sits higher on the shoe.
This is the main reason a hem length that looked correct on a wider trouser looks wrong on a slim one cut to the same measurement.
Shoe height shifts the reference point
The hem rests on whatever is beneath it. A thick-soled boot raises the contact point and reduces break; a low slipper lowers it and increases break.
Hemming is therefore done wearing the shoes the trousers will be worn with, and a wardrobe spanning boots and loafers cannot be served by one length.
Cuffs add weight at the hem, which pulls the fabric down and produces a cleaner fold than an uncuffed leg of the same length.
Fabric decides how the fold behaves
Heavier woollens hold a fold and produce a defined, stable break that looks the same after a full day of wear as it did in the morning.
Lightweight cottons and linens crumple rather than fold, so excess length reads as untidiness instead of as a deliberate break.
Which is why summer trousers are usually hemmed shorter, and why the same length in flannel and in linen produce quite different impressions.
The convention has moved and will move again
Fuller cuts historically carried a substantial break because wide legs demanded length to hang correctly against the shoe.
Slimmer cuts pushed hems up until no break at all became normal, which suited a narrow opening but exposed more sock.
As wider legs return, hems lengthen again, and the shift is a mechanical requirement of the silhouette rather than a change in taste for its own sake.