Fit, measuring and alterations · 8 October 2026 · 3 min read
Why do my trousers sag at the seat?
Trousers baggy at the back usually have a rise too long, a seat cut too full or a fabric that stretches. How to tell which, and the measurements that correct it.
InspirationToo much fabric with nowhere to go
Trousers sag at the seat when there is more length or width behind you than your body fills. Usually the back rise is too long, or the seat is cut for a rounder shape than yours; sometimes the cloth itself stretches as the day goes on. The spare fabric has nowhere to go, so it folds under the seat and hangs.
This is a fitted-trouser problem. A traditional shalwar is meant to be full at the seat, and folds there are part of the style. On straight trousers or cigarette pants, they are not.
The three usual causes
Each one leaves a slightly different mark, which helps when you describe it.
- A back rise that is too long. The rise is the depth from the waistband to the crotch seam. When the back part is longer than your body needs, the extra length collects as horizontal folds just under the seat.
- A seat cut too full. Trouser patterns curve the back seam to make room for the seat. If yours is flatter than the pattern assumes, there is more width than you fill, and the fabric hangs in loose vertical slack.
- Fabric that grows. Linen, viscose, loosely woven cottons and anything with a little stretch relax with body heat and movement. Trousers that look neat in the morning and baggy by the evening are usually doing this.
Reading the folds in a mirror
Stand side-on to a mirror, or ask someone to take a photo of you from the side and from behind, in the trousers that sag. Folds running across, under the seat, point to too much length. Loose fabric you can pinch out vertically at the centre back points to too much width. Diagonal folds running from the inner thigh up towards the seat often mean the crotch curve is shaped for a different body, which is worth mentioning even if you cannot name it.
Check again after a few hours of wear. If the folds appear only later, the fabric is a large part of the story, and a firmer weave will help as much as any measurement.
The measurements that correct it
Start with the trouser measurements on our trouser size guide: waist, hips, length and trouser bottom. Then add the two that control the seat. The seated rise is taken sitting upright on a hard chair, from your waist down the side of your body to the seat. The full crotch length runs from the centre front of your waist, down between your legs and up to the centre back, with the tape snug.
Add a note in plain words, for example “flatter seat, ready-made trousers bag under the seat”. If you have a pair whose seat sits well, lay it flat and measure it as in our guide to measuring clothes that fit you. If you have the opposite problem, trousers that pull when you sit, see why trousers pinch when you sit down.
When you send your enquiry, these details are written into your quote before cutting. The Fabric + Stitching page explains ordering with our fabric if you do not have your own.
Common questions
Does a baggy seat mean the trousers are too big?
Not necessarily. The waist and hips can be exactly right while the seat is still too long or too full, because the rise and the seat curve are separate parts of the pattern from the waist and hip widths.
Will a stretch fabric fix it?
Usually not. Stretch can make the problem worse, because the fabric relaxes further as you wear it. A firm, stable weave holds its shape through the day.
Do I need to give my crotch length?
It is optional, but for fitted trousers it is one of the most useful extra numbers you can send, along with the seated rise, because both describe the seat directly.
