How to Alter a Pattern for Sleeves That Fit AND Flatter

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If you find that some patterns are a tad too snug in the sleeves, don’t blame your arms — they’re just fine! The problem is the pattern. Commercial patterns are designed to fit average proportions. And not everyone is average, or wants to be. Fortunately, reworking the upper arm of a pattern to fit your dimensions is a quick and easy fix.

Just follow this simple pattern-alteration tutorial. You’ll thank us later when your arms look smokin’ and you can actually do a cartwheel in your finished garment. Not that you would. But it’s nice to know you could.

How to Adjust a Pattern's Upper Arm

1. Measure Your Arm and Compare It to the Pattern

If possible, recruit a helper for this. With your arm relaxed at your side, measure around your bicep at its fullest point, usually right at your underarm. Add 1½ to 2 inches for ease of movement if you’re working with a woven fabric; about 1 inch is fine for a knit. If you’re making a winter coat or jacket, you may want to add a bit more ease so you can wear it over a sweater.

Now take a look at your sleeve-cap pattern. Some patterns have the finished bicep circumference measurement printed on the pattern. If yours doesn’t, no problem. Just measure horizontally from seam allowance to seam allowance at the underarm.

Note the difference between the two numbers. This is how much width you want to add to the upper arm of your pattern.

2. Trace the Original Sleeve Cap

To make the sleeve adjustment, you’ll need to alter your pattern piece. If you’d rather not cut the original, trace it and do the adjustments on the copy.

Draw two lines on your pattern piece: one (line A above) going horizontally from seam allowance to seam allowance at the underarm, another (line B above) perpendicular to the first that goes right down the middle of the pattern from the center shoulder to the bottom. Then pin your sleeve to a piece of paper and trace the entire sleeve cap as shown.

3. Spread the Sleeve

To adjust the sleeve width at the bicep, cut through the vertical and horizontal lines you just made up to — but not over! — the seam allowance. Now spread the sleeve pattern apart the amount you want to add (if you need an extra inch around the bicep, for example, you’ll want to expand it a ½ inch on each side). To make the pattern easier to pivot, you may also want to cut a little snip into the seam allowance on each side — just don’t cut all the way through.

Note: When you spread the pattern apart, the sleeve cap gets pulled down. Don’t worry about this! Since you traced the original sleeve cap in Step 2, that shape remains intact and the sleeve will still match the original armhole on the pattern.

4. Adjust the Bodice Front and Back

By spreading the sleeve apart to make more room, you also add to the seamline on each side of the sleeve cap. If the increase totals more than an inch, you’ll need to add some width to the front and back bodice in order to fit the new sleeve into the armhole.

There are two ways to do this. One is to add at the underarm and gradually taper to nothing at the waist (as above).

The other option is to deepen your armhole slightly at the underarm (as above); this will make the armhole seam line a bit longer to match the new sleeve-cap seam line.

A final tweak: Since you’ve added some width to the upper portion of your sleeve, you may want to taper the sleeve seam a bit so it blends with the width on the lower part of the arm.

And that’s it! Now sew up your garment and show off those gorgeous arms!

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How to Alter a Pattern for Sleeves That Fit AND Flatter