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Seam Allowances: a Guide to Alterations in Tailoring

Words and Illustrations by Jeffery Diduch

Alterations are a fact of life when buying tailored clothing. No two bodies are alike and seam allowances are necessary and provided so that a garment can be altered to fit better. Likewise, bespoke garments will also have seam allowances built in to allow for changes in weight over the life of a garment. The types of seam allowances, or inlays, will vary whether the garment was ready-made or tailor-made and so the types of possible alterations will also vary.

We will look in-depth at the allowances given for garment alterations. The illustrations show typical seam and inlay allowances – where bespoke differs from RTW; the extra is shown shaded in grey. Exact amounts vary from cutter to cutter so no detail has been given. Keep in mind that the minimum seam allowance recommended is ¼” so when looking at an allowance of 1”, for example, you have ¾” left to let out. Also, keep in mind that were are discussing one half of the garment so allowances should be doubled in most cases. For instance, if we can let the waist out 1/2” at a certain place, it gives a total circumference of 1” to let out.

coat back seam allowances tailor measurements let out bring in how much

Manufacturers vary slightly on the allowances on the neck, center back and side seam.

Neck
there may be only 3/8”, but better makers will have 5/8” allowing the collar to be raised up to 3/8”.

Shoulder
There is no allowance for changes to the shoulder width: it can be narrowed but not widened. Bespoke garments will generally have an allowance for widening here. The shoulder can be sloped or squared (squaring will shorten the garment slightly).

Center back
Between 5/8” and 7/8” is typical – bespoke cutters may leave more here.
Total to let out – ¾” to 1 ¼”

Side seam
Between 5/8” and 7/8” (bespoke may have less here).
Total to let out here – ¾” to 1 ¼”.

Hem
Generally 1 1/8” to 1 ¼”. Bespoke garments may have more. We will see that in most cases this does not allow the garment to be lengthened, but does give us some wiggle room for passing up the back for a stooped figure.

seam allowances tailoring suit pants trousers allowance tailor measurements let out bring in how much side body Armhole
RTW has only a small allowance for changes at the side seam. Bespoke generally has a generous allowance to either increase or decrease the width of the armhole. The armhole CAN NOT be raised without altering the length of the jacket and the position of the gorge and the pockets. While not strictly impossible, raising the armhole should not be attempted on a finished garment.

Side seam
Between 5/8” and 7/8”. Bespoke will have considerably more.
Total to let out here – ¾” to 1 ¼”

Front seam
Generally 5/16” or 3/8”- no room to let out here. The pocket will intersect this seam so in most cases it must be dismantled and remade in order to take in this seam here; this is difficult and costly.

Hem
Generally 1 1/8” to 1 ¼”. Bespoke may have more.

seam allowances tailoring trousers suit blazer sport coat

front jacket allowance tailor measurements let out bring in how muchNeck
There may be only 3/8”, but better makers will have 5/8” allowing the collar to be raised up to 3/8”.

Shoulder
There is no allowance for altering the shoulder in RTW garments, other than to narrow it, slope it, and, to a small extent, to square it. Bespoke generally has an allowance to drop the front (for a longer front balance) and to widen the shoulder. Crookening and straightening the shoulder (to a small extent) is also possible in bespoke garments.

Side seam
Generally 5/16” or 3/8” – no room to let out here. The pocket will intersect this seam so in most cases it must be dismantled and remade in order to take in this seam here; this is difficult and costly.

Hem
Generally 1 1/8” to 1 ¼”. Notice how the front edge is cut off where the curved edge meets the hem- this prevents lengthening the garment in a consistent, back-to-front manner, impossible.

Lapel and front edge
It is sometimes possible, though costly, to narrow the lapel – the buttonhole creates certain restrictions. It is not possible to widen it. In some cases, a peak can be converted to a notch, though never the reverse. The lower part of the front edge can be cut away more beneath the lowest buttonhole.

seam allowances tailoring trousers suit blazer sport coat

top sleeve jacket allowance tailor measurements let out bring in how muchHem
Generally 2” to 2 ¼” given to lengthen the sleeve from the cuff – no allowance is given to lengthen from the top, but the sleeve can be shortened from the top.

Inseam, elbow seam
The sleeve can be narrowed (should really be done at the elbow seam) but no allowance is given to widen the top sleeve: extra width would be necessary to correct most sleeve “divot” problems so it is best not to attempt to have those altered.

Vent
Some RTW garments have a narrow vent, others have a wider vent. Making functional buttonholes on a narrow vent is impossible without either narrowing the sleeve or piecing in more cloth.

seam allowances tailoring trousers suit blazer sport coat styleforum

undersleeve jacket allowance tailor measurements let out bring in how muchHem
Generally 2” to 2 ¼” given to lengthen the sleeve from the cuff. No allowance is given to lengthen from the top, but the sleeve can be shortened from the top.

Inseam
No allowance for changes given here.

Elbow seam
No allowance is given in RTW (Oxxford is the only manufacturer that I am aware of who do give an allowance here) but bespoke will generally have seam allowances for widening or narrowing the armhole, as well as widening the bicep and elbow. The cuff can be narrowed.

seam allowances tailoring trousers suit blazer sport coat

trousers pants allowance tailor measurements let out bring in how muchNo allowances for enlarging the trouser front are given in RTW; bespoke often has seam allowances to lengthen the rise from the waist.

The leg can be narrowed easily; narrowing at the hip requires recrafting the pocket.

seam allowances tailoring trousers suit blazer sport coattrousers pants back allowance tailor measurements let out bring in how much Waist
Generally, 1 ½” given to let out the waist.
Total to be let out 2 ½”.

Outseam
RTW trousers have no allowance to let out the outseam, most bespoke trousers do.

Inseam
Generally 1 1/8” to let out the back thigh, bespoke may have more. In most cases, this allowance is tapered to nothing at the knee, though some manufacturers extend it all the way down to the hem.

seam allowances tailoring trousers suit blazer sport coat


If you’re thinking about altering a garment and need some advice, check out the Tailor’s Thread: Fit Feedback and Alterations on Styleforum.

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2 Comments

  1. CHIN-CHEN LEE

    May 13, 2018

    awesome general info

  2. Peter Zottolo

    Peter Zottolo

    May 15, 2018

    Articles like this are why I love StyleForum. Thanks Jeffery 🙂

Comments are closed.