Two people carry a jacket into the same alterations shop on the same afternoon. The first wants the waist brought in by three centimetres and leaves with a ticket and a Thursday collection time. The second wants the waist opened out by two centimetres and is turned away. Same counter, same machinist, same skill on the same machine. What separated them was decided months earlier by whoever cut the cloth, and the evidence is folded inside the garment where neither customer thought to look.
Tailors call that hidden margin the inlay. Pattern drafters call it seam allowance. Either way it is the strip of fabric sitting beyond the stitch line, pressed flat and out of sight. Narrowing a garment only asks for a new stitch line further in, and there is always somewhere further in to go. Widening one asks for cloth that already exists inside the seam. If a factory trimmed that margin to five millimetres and locked the raw edge with an overlocker, the width you now want was cut away and binned before the garment ever reached a hanger.
Taking in is cheap, letting out is a gamble
The asymmetry catches people out because both jobs sound like the same job. They are not. Bringing a side seam in is subtractive work with a predictable price, and a shop can quote it across the counter without opening anything up. Letting a side seam out is an inventory question first and a sewing question second, and nobody can answer it while the garment is still on your body.
There is a second cost people forget. A seam that has been let out often keeps a shadow of its old stitch line, especially on dark cotton, pressed wool, or anything with a surface finish. The needle holes close up unevenly and the crease where the fold used to sit can stay visible after pressing. That mark is not a mistake by the shop. It is the fabric remembering two years of being folded one way.
Turn it inside out before you decide you love it
The inspection takes less time than reading the care label. Reach into the garment, find the side seam, and pinch the two layers of spare fabric beyond the stitching between your thumb and finger. On better tailoring you will feel a generous flap that folds back on itself. On a garment built to a tight cost you will feel almost nothing, and a thin bound edge where the allowance should be.
Look at how the raw edge was finished, because the finish tells you the intention. A pressed-open seam with two separate edges, each finished on its own, is a seam that was meant to be reopened one day. A seam where both layers were trimmed together and wrapped in a single line of overlocking was never built for a second life. That single wrapped edge is faster to sew and uses less cloth, which is exactly why it is everywhere.
Eight seam classes, and only some can be reopened
None of this is folklore. Seam construction has been formally catalogued for decades. ISO 4916, Textiles, Seam types, Classification and terminology, in its second edition approved on 12 September 1991 and still listed as valid, sorts stitched seams into eight classes and gives each construction a five-digit designation. It runs to 64 pages, and it is read alongside ISO 4915, which does the same job for stitch types.
The useful idea for a shopper is not the code itself but what the classes are sorted by: how many layers of material meet, whether their edges are enclosed, and how they sit relative to each other. A construction that encloses both edges inside a fold, or binds them in a separate strip, has committed the allowance to holding the seam together. Opening it means unpicking the finish as well as the seam, and often there is no usable width underneath once you do.
Where the spare cloth hides, garment by garment
Inlay is not distributed evenly. It clusters at the seams a cutter expected somebody to adjust, and it is thin or absent everywhere else. That is why a shop will happily move a trouser waist and refuse to touch a shoulder.
| Garment | Seam that usually carries inlay | Change that is rarely possible |
|---|---|---|
| Trousers | Centre back seam below the waistband, plus the side seams | Widening the thigh or opening the front rise |
| Tailored jacket | Side seams, centre back, sleeve seam near the cuff | Adding width across the chest or moving the shoulder point out |
| Shirt | Side seams on a fused or pressed-open construction | Anything on a flat-felled side seam, or adding collar length |
| Skirt or dress | Side seams and the seam either side of the zip | Letting out a bias-cut panel or a lined princess seam |
| Knitwear and jersey | Very little, since edges are usually overlocked together | Almost any increase in width or length |
France published a price list for repairs
Repair economics stopped being guesswork in one country, and the numbers are public. France introduced a repair bonus for clothing and footwear on 7 November 2023, funded by eco-contributions from brands and applied as an immediate discount at approved repairers. The official guidance sets a floor of twelve euros on the repair before any discount applies, caps the total reduction at 60 per cent of the repair price, and lists fixed amounts by job, including seven euros for patching a hole in a garment and between ten and twenty-five euros for changing a lining depending on how involved it is. The stated goal is to move France from 16 million items repaired in 2019 to 21.6 million by 2028.
Read the list of covered jobs and one absence stands out. The scheme pays toward mending what has broken. It does not pay toward altering what never fitted, because that is not damage. A hole in a sleeve is a documented repair with a documented price. A waist that needs two centimetres it never had is a design limit, and no subsidy can put cloth back inside a seam.
The two-minute check at the fitting room mirror
Do this on anything you expect to keep for years, or on anything that fits in most places and misses in one.
- Find the side seam and pinch it. Two comfortable layers folded back mean a tailor has something to work with. A thin wrapped edge means the answer will be no.
- Check the seam you actually need moved. Generous inlay at the waist is no help if the problem is the chest, and the two seams are often built to different rules.
- Look for a pressed centre back seam on trousers. This is the classic reserve, and it commonly holds a couple of centimetres in total across the two sides.
- Treat overlocking as a closed door. If both raw edges are wrapped together in one pass, plan around the size on the label rather than around an alteration.
- Buy the size that needs taking in, not letting out. Where two sizes are close and neither is right, the larger one keeps the decision open.
Ask about the inlay before you ask about the price
The next time you take something to an alterations counter, lead with the inlay rather than the outcome. Ask how much spare fabric the seam is carrying and where, then decide what to request. A shop that measures before quoting is giving you real information, and a quote given without the garment being opened is a guess you will pay for either way.
None of this argues for buying only expensive clothes. Plenty of well-cut garments carry thin allowances, and plenty of costly ones do too. It argues for one extra movement of your hand before the card comes out. The label tells you a size somebody chose, and the seam tells you how much that size can still change.