Seam Allowance: Standard Sizes and How to Sew It Even

Seam allowance is the strip of fabric between the cut edge and your line of stitching. Every pattern assumes one width, and the garment only comes out the size on the envelope if you sew that width. The catch for beginners is that the width is not universal, and the cost of getting it wrong grows with every seam.

What the pattern companies actually say

There is no single standard. Here is what five sources state, in their own words, about the allowance built into their pieces.

SewDirect's Simplicity guide gives the 5/8-inch figure and says any other amount is marked on the piece. Seamwork's help centre splits wovens and knits. Named's basic instructions say its patterns usually include 1 cm and never ask you to add any. BurdaStyle's seam allowance page says plainly that burda patterns do not come with them.

The error multiplier: why 1/8 inch matters

A seam takes fabric from two edges at once. Sew 1/8 inch wider than the pattern assumes and that seam removes 1/4 inch from the garment's circumference. Multiply by the seams that run around the body and it adds up fast. This is our own arithmetic, so you can check it with a tape measure.

The last column is the mix-up case: sewing a 5/8-inch pattern at 3/8 inch because the last pattern you used was a knit or a Named design. On a seven-seam bodice, that is 3 1/2 inches of room you never planned for.

Burda makes the same point from the other side. Its seam allowance page works through a dress with three seams and says cutting it without allowances leaves it 9 to 12 cm tighter.

Quilters feel it even more

Piecing seams are short and many. Picture a block made from four strips cut 3.5 inches wide, joined with three seams. At a true 1/4 inch it measures 12.5 inches across. Sew each seam 1/16 inch too wide and it comes out 12 1/8 inches. Five of those blocks in a row are 1 7/8 inches short before you even join them.

That is why the BERNINA team's guide to accurate quarter-inch seams asks for a scant 1/4 inch, a thread or two narrower, to account for the width the seam itself takes up.

How to sew an even allowance

Most beginners watch the needle. Watch the edge of the fabric instead, against a guide that is already the right distance away.

1. Find the lines on your needle plate. Most machines have engraved lines to the right of the needle. They are usually measured from the needle in its centre position, so if you move the needle left or right, every line moves with it.
2. Check the line before you trust it. Measure from the needle to the line with a 6-inch sewing gauge. Its slider locks, so you can set it once and check every seam. It sits on our marking and measuring shelf.
3. Add a ledge if the lines are faint. A few layers of masking tape along the right line give the fabric edge something to ride against.
4. Sew slowly and steer from the front. Your hands guide the fabric into the foot. Pulling from behind changes the line.

For quilting, a dedicated quarter-inch foot puts the 1/4 inch at the edge of the foot itself. Some machines include one and some do not, so check your manual's accessory list first. If you are still choosing a sewing machine, that list is worth reading before you buy.

Test it on scraps, not the project

• Garment allowance: sew a 5-inch line on two scraps, then measure from the stitching to the edge at three points with the gauge. All three should match the pattern.
• Quilting allowance: cut three strips 1.5 inches wide and sew them side by side. Press, then measure the middle strip. At a true 1/4 inch it reads 1 inch exactly. Wider than 1 inch means your seams are too narrow. Narrower means they are too wide.

A clear quilting ruler such as the Fiskars 3 x 18 inch ruler makes that last measurement quick, because you can see the seam lines through it.

Gear mentioned above

What we'd buy for this

One pick per category, chosen from the research pages linked in this piece. Borrow before you buy — nothing here is required to start.

• 
  Marking & Measuring

  Fiskars 6-Inch$12.79★ 4.7 out of 5 stars · 405 ratings

  Measuring and repeating hems, seam allowances and buttonhole spacing. The slider locks at 1/8-inch steps, so every hem in a row turns up the same, and one end is a corner turner.

  Why this oneBuy
• 
  Sewing Machines

  Brother XM2701$149.00★ 4.6 out of 5 stars · 19,332 ratings

  A first machine — 27 built-in stitches is enough to sew clothes without a menu to decode, and the listing specifies the automatic needle threader and the jam-resistant drop-in top bobbin, which are the two steps beginners most often give up on.

  Why this oneBuy
• 
  Quilting Rulers

  Fiskars$8.97★ 4.8 out of 5 stars · 3,291 ratings

  Priced in the lower half of this category; the listing claims a non-slip surface, which is the difference between a straight cut and a ruined strip.

  Why this oneBuy

Researched from listings, specs and owner feedback — never hands-on testing. We may earn a commission; it never changes a pick.

Adding allowance to a pattern that has none

If you use a burda sheet or a pattern you drafted yourself, you add the allowance before cutting.

• Trace first. Copy your size onto tracing paper so the original sheet stays usable.
• Mark a parallel line. Set the sewing gauge to the width you chose and mark dots every inch or so around each stitching line, then join them. Tailor's chalk works straight onto fabric if you skip the paper step.
• Pick one width and write it down. BurdaStyle suggests at least 1.5 to 2 cm. Write your choice on every piece, because you will forget by the time you sew.
• Hems are separate. A hem allowance is usually deeper than a seam allowance. The pattern or your own plan should say how much.

After the seam: trim, clip or keep

The allowance is not finished once you have sewn it.

• Keep it on straight seams in garments. A full allowance gives you room to let a seam out later, and to finish the raw edges. Our guide to finishing seams without a serger covers five ways.
• Trim it inside collars, cuffs and corners so the turned piece lies flat.
• Clip it on inward curves, like a neckline, so the curve can spread when turned.

If you are still working out what the symbols on a pattern piece mean, how to read a sewing pattern walks through them. A wonky seam on a practice scrap costs nothing, and it is how everyone finds their line.