A gaping armhole has more edge length than your body needs at that point, almost always at the front, where the pattern expects a fuller bust or a more forward shoulder than yours. The fix is to pinch out the excess on a toile as a small wedge pointing at the bust, then transfer that wedge to the pattern and rotate it into an existing dart or the side seam; 1 to 2 cm (3/8 to 3/4 in) is typical. Taking in the shoulder seam does not solve it, because it shortens the armhole from the top and tightens everything else.

Why do armholes gape?

The armhole is a curve, and part of that curve runs over the bust at the front and the shoulder blade at the back. On a pattern, the length of that curve is set by the size's bust measurement and bust prominence. If your bust is smaller than the pattern assumes, or sits lower, the fabric that was meant to travel over the curve of the bust has nowhere to go and stands away from the body in a loose fold at the front armhole.

The same happens at the back when the pattern allows for more shoulder blade shaping than you need, or when your shoulders slope more than the pattern's. A sleeveless top shows the problem clearly; a sleeve hides it a little, but the fold is still there under the sleeve cap and shows as a diagonal wrinkle.

Gaping is a shaping problem, not a width problem. That is why a smaller size rarely helps: it tightens the bust and waist and leaves the gap where it was.

How do you tell gaping from a size that is too big?

Put the garment or toile on and look at it in a mirror, side on. Pinch the loose fabric at the armhole between finger and thumb and watch what happens elsewhere.

  • If the pinch closes the gap and the rest of the bodice still fits, the problem is shaping, and a dart rotation will fix it.
  • If the whole front is loose across the bust and under the arm too, the size is too big: compare your bust with the finished garment measurement and go down a size, or draft to your own measurements.
  • If the gap closes when you lift the outer end of the shoulder seam, the cause is the shoulder. Then the sloping shoulders adjustment is the one you need.

How much do you need to take out?

Wear the bra you will wear with the garment. Pinch the excess at the armhole into a fold that points toward the bust point, the fullest point of the bust, and pin it. The fold should lie flat against the body with no pull at the shoulder or the side seam. Measure the depth of the fold at the armhole edge with a tape and double it: that is the total amount to remove. A 1 cm (3/8 in) fold means a 2 cm (3/4 in) wedge.

Mark on the toile where the fold starts on the armhole edge, usually about a third of the way down from the shoulder. Take the toile off and transfer the mark and the amount to the pattern.

How do you fix a gaping front armhole on the pattern?

This is a dart rotation. The wedge you pinched becomes a temporary dart in the armhole, and you move it into a dart the pattern already has, so the armhole gets shorter and the existing dart gets a little deeper. Nothing changes in the bust or waist width.

  1. Mark the gap. On the front bodice pattern, mark the point on the armhole where the fold started and draw a line from it to the bust point.
  2. Draw the wedge. Along the armhole edge, measure the total amount (say 2 cm) from that mark toward the underarm, and draw a second line from this point to the bust point. The triangle between the two lines is the armhole dart.
  3. Open the receiving dart. Draw a line from the bust point through the middle of the side bust dart (or the waist dart on a fitted bodice) to its seam. Cut along it up to the bust point, leaving a paper hinge at the point.
  4. Close the armhole dart. Cut along one leg of the armhole dart and overlap it onto the other leg, taping it shut. The cut from step 3 opens by the same amount: the side dart is now deeper.
  5. True the lines. Redraw the armhole in a smooth curve across the closed wedge. End the dart 2 to 3 cm (3/4 to 1 1/4 in) short of the bust point as usual so it does not finish in a pucker. Fold the new dart closed on paper and cut the seam edge through the fold so the dart legs match.
  6. Check the facing or binding. Trace the armhole facing from the new armhole; cut a bias binding to the new length.

On a dartless block, such as a shell top, rotate the wedge into the side seam at the underarm and ease the extra length into the seam, or into the waist as a little flare. If the amount is under 1 cm, skip the paper work and ease the edge in instead: see the section on garments already cut.

How to sew darts covers pressing the deeper dart so it lies flat.

How do you fix a gaping back armhole?

At the back, the gap sits lower, around the shoulder blade, and the fix is the same idea: rotate the wedge into a back shoulder dart or into the shoulder seam as ease. Most back bodices already have 0.5 to 1 cm (1/4 to 3/8 in) of ease along the shoulder seam, sewn in by stretching the front shoulder to fit. A wedge of up to 1.5 cm (5/8 in) can be added to that ease. More than that calls for a back shoulder dart, 6 to 8 cm (2 3/8 to 3 1/8 in) long, pointing toward the shoulder blade.

If the gap closes when you lift the outer end of the shoulder seam, your shoulders slope more than the pattern's and the shoulder seam needs to drop at the armhole end. That takes about 1 cm out of the armhole depth, so lower the underarm point by the same amount to keep the armhole the same length for the sleeve.

Can you fix gaping on a garment that is already cut?

Yes, for small amounts. Under 1 cm (3/8 in), sew a length of stay tape or narrow fusible tape to the armhole seam allowance, cut 1 cm shorter than the curve, pulling the fabric to fit the tape as you stitch. The armhole tightens evenly and the binding or facing goes on as usual. On a bound armhole you can also stretch the bias binding slightly while applying it over the gaping section; it draws the edge in as it relaxes.

For a larger gap on a sleeveless garment, open the side seam and sew a small dart, about 1.5 cm wide, through the armhole seam allowance and the facing together. It becomes a short seam in the finished edge. It is visible on a plain fabric; on a print it disappears.

Why do armholes gape less with a made-to-measure pattern?

A pattern drafted from your own bust, waist and shoulder width puts the armhole where your body is, so the most common cause, a pattern sized for a bigger bust than yours, is handled before you print. Sewly drafts every bodice from your measurements rather than from a size chart. What a measurement cannot capture is the shape between two numbers: how prominent the bust is, whether the shoulders slope or roll forward. Those still show on a toile, and the dart rotation above is how you correct them, on any pattern. Make a toile of the bodice before cutting your fabric whenever the armhole will be sleeveless and finished with a facing, because that is where a gap shows most.