Full bicep adjustment: sleeves that do not pull

A full bicep adjustment adds width to a sleeve across the upper arm while leaving the sleeve cap, and so the armhole it has to fit, almost unchanged. You need it when the sleeve shows tight horizontal folds across the bicep, rides up when you lift your arm, or has less than about 5 cm (2 in) of ease over your arm in a woven fabric. The alteration takes ten minutes: measure your bicep, compare it with the sleeve at its widest line, slash the pattern down and across, spread it by the difference, and check the result on a toile.

How do you know you need a full bicep adjustment?

The signs are all on the upper arm, between the shoulder and the elbow:

• Horizontal drag lines across the bicep, tight folds that point toward the front and back of the arm. They are the sleeve straining around the arm.
• The sleeve rides up when you raise or bend your arm and does not fall back down.
• The underarm seam strains or the stitches show when you bend the elbow.
• Marks on your skin after an hour of wearing, where the sleeve edge pressed in.
• The bodice pulls too. A sleeve that is too narrow drags on the armhole, so you may also see folds radiating from the underarm into the bodice.

If the folds are diagonal and start at the shoulder point, the problem is more likely the shoulder width than the arm. How to read drag lines sorts the two apart. A sleeve that is too narrow is a common complaint among people with muscular arms, soft upper arms, or a bust size that puts them in a smaller pattern size than their arms would take.

How much ease does a sleeve need at the bicep?

Measure your bicep around the fullest part of the upper arm, with the arm relaxed and slightly bent. Then measure the pattern. Lay the sleeve flat and draw a horizontal line from underarm seam to underarm seam at the widest point, directly under the cap. That is the bicep line. Measure it between the stitching lines, not the cutting lines, so the seam allowance is left out.

The difference between the two numbers is your ease. How much you need depends on the fabric and the garment:

If your pattern gives you 2 cm (3/4 in) where you want 6 cm (2 3/8 in), you need to add 4 cm (1 5/8 in). That is the amount you will spread.

How do you widen a sleeve pattern without changing the armhole?

The classic method spreads the sleeve at the bicep while the cap stays hinged at the top, so the length of the seam that joins the armhole hardly changes. Trace the sleeve before you start, and work on the copy.

1. Draw the vertical line. From the dot at the top of the cap straight down to the hem, parallel to the grainline. On a two-piece sleeve, work on the upper sleeve and divide the amount between the two pieces.
2. Draw the bicep line. The horizontal line from underarm to underarm that you measured earlier.
3. Cut the vertical line from the hem up to the cap seam line, and stop there. Leave a hinge of paper at the top: do not cut through.
4. Cut the bicep line from the vertical cut out to each underarm seam line, and stop at the seam line on both sides, leaving two more hinges.
5. Spread the center. Slide the two halves apart at the bicep line until the gap equals the amount you need, 4 cm in our example. The two cap pieces swing outward from the hinge at the top; the two lower pieces follow, and the horizontal cuts overlap a little near the center. Tape paper behind the gap.
6. True the lines. The cap is now a fraction lower, which is fine for up to about 2.5 cm (1 in) of added width. The sleeve has lost a little length where the horizontal cuts overlapped: measure how much at the center and add it back at the hem. Redraw the underarm seams and hem as smooth lines.

For more than 2.5 cm, the cap would drop too far and the sleeve would lose its lift. Split the amount: do this alteration for the first 2.5 cm, then add the rest at the underarm seams. Add a quarter of the remaining amount to each side of the sleeve at the bicep line, tapering to nothing at the cap notches and the wrist. That lengthens the underarm part of the cap seam, so lower the bodice armhole at the underarm by the same amount, split between front and back, and blend into the side seam.

Tip: Measure the cap seam before and after with the tape on its edge. It should match the armhole plus the cap ease the pattern was drafted with, usually 2–3 cm (3/4–1 1/4 in) on a woven. If it has grown by more than 1 cm (3/8 in), ease it in or take the difference out of the sleeve cap height.

What else changes with a wider sleeve?

The hem of the sleeve is wider than before by the amount you spread, unless you taper the lower sleeve back to the original wrist. Decide which you want. A long sleeve on a blouse usually looks better tapered back to the original cuff: redraw the underarm seams from the bicep line to the original wrist points. A short sleeve can keep the extra width to the hem, or taper half of it out.

Any cuff, sleeve facing or sleeve lining must be altered the same way. A placket on the lower sleeve does not move.

Sew a toile before cutting your fabric, even if the numbers say the sleeve is right. Making a toile shows how to check the sleeve: raise your arms, fold them, reach forward. The arm should move without the bodice following.

Does a made-to-measure pattern still need a full bicep adjustment?

A standard-size pattern gives every size a sleeve width tied to the bust size, which is why a size 42 with a size 46 arm has to alter it. A pattern drafted from your own measurements sets the sleeve width from the numbers you enter, so the gross width problem is handled before you print anything. Sewly's made-to-measure drafting works that way, and the measuring assistant explains where to put the tape for each measurement.

What the numbers do not say is where the fullness sits on your arm and how you carry your arms, so a toile is still worth the half hour. If the sleeve is wide enough but still pulls, look at the cap height and the shoulder: a narrow shoulder adjustment or a broad back adjustment solves more arm complaints than people expect.