How to Make a Full or Narrow Bicep Adjustment

Do your sleeves often feel a little too snug around your upper arm? Or perhaps you find that there's more fabric than you need and your sleeves feel a bit roomy? Not to worry - you can adjust the width of a sleeve pattern to get a more comfortable fit on your me-made garments.

A full bicep adjustment adds width around the upper arm, while a narrow bicep adjustment removes width. Both use the same basic method: split the sleeve pattern, move the pieces apart or together, and then smooth out the new shape.

This can be particularly useful when you're making outerwear, such as our Manon jacket or Sonny jacket, where getting enough room through the upper arm is important for comfort and layering. You can use the same technique on other garments, such as the straight sleeve version of the Nell blouse and dress, and even on patterns designed for stretch knit fabrics, such as the Pearl cardigan.

In this tutorial, we'll show you how to make both wide and narrow bicep adjustments to a one-piece sleeve.

Do you need a bicep adjustment?

Before altering your sleeve pattern, it's worth checking whether you actually need to.

With your arm relaxed, measure around the fullest part of your upper arm. Compare this measurement with the bicep measurement for your pattern - if it's not provided, you can simply measure the sleeve pattern piece across its widest point, subtracting the seam allowance on each side (15mm or 5/8in for most home sewing patterns).

Remember that the finished sleeve measurement includes ease – the extra room between your body and the garment. A jacket sleeve may need more ease than a close-fitting top, particularly if you want to wear layers underneath.

For woven garments, a sleeve should have somewhere between 2cm to 7.5cm (1in to 3in) of ease around the bicep.

If you’re working with a pattern that calls for stretch knit fabric, you may find that the sleeve doesn’t have any bicep ease, or even has negative ease - in other words, the pattern piece is smaller than the body if it's designed to be very close-fitting.

If there’s a considerable difference between your bicep and the pattern’s bicep measurement, a bicep adjustment could be just the ticket to get that sleeve fitting you nicely.

How much do you need to add or remove?

First, work out how much you need to alter the sleeve pattern by.

Calculate:

Your bicep measurement + desired ease − pattern bicep measurement = amount to add or subtract

For example, if your bicep measures 38cm, you'd like 5cm of ease, and the pattern measures 41cm:

38cm + 5cm − 41cm = 2cm to add

If the resulting number is positive (e.g. 2cm), that's how much to add with a full bicep adjustment. If it's negative (e.g. -2cm), you'll be taking excess width away with a narrow bicep adjustment.

Remember, this is the total amount to add around the circumference, not the amount to add to each side of the sleeve.

How to make a full bicep adjustment

1. Mark the sleeve

Trace off a copy of your sleeve pattern piece, making sure to copy over all the pattern markings. On your traced sleeve, mark the stitching lines 15mm (5/8in) in from the edge of the pattern piece, and the hemline (check the hemming instructions for the pattern you are making).

Draw a line from the centre of the sleeve head down to the hem, parallel to the grainline – we’ll call this line 1.

Next, draw a second line across the sleeve at the widest part of the bicep, at a right angle to the first line – this is line 2.

2. Cut the pattern

Starting at the hemline, cut along line 1, stopping just before the stitching line at the sleeve head. From the other side of the sleeve head stitching line, cut through the remainder of line 1, stopping just before the stitching line to leave a little “hinge”.

Then cut along line 2 from the centre towards each side, again stopping just before the stitching lines at the underarm seams. From the other side of the underarm seam stitching lines, cut through the remainder of line 2, stopping just before the stitching lines to create two more “hinges”.

3. Spread the sleeve

Place some new paper underneath your sleeve.

Keeping the bottom of the sleeve in place, gently spread the pieces apart. A gap will open through the centre of the sleeve. Continue spreading until the gap at the bicep measures the total amount you need to add.

Tape the pieces in place.

4. Smooth the pattern

The sleeve head and hem may have become a little wonky after being spread apart. Draw a smooth curve over the sleeve head, blending it into the original shape.

Check the hem and underarm seams too, and straighten them if needed.

How to make a narrow bicep adjustment

If your sleeve has more room than you need, you can use a similar approach – but instead of spreading the pieces apart, you'll bring them closer together.

1. Mark and cut the sleeve

Trace off a copy of your sleeve pattern piece, including the pattern markings. Mark and cut lines following steps 1 and 2 of the full bicep tutorial above.

2. Overlap the pieces

Instead of spreading the sleeve apart, move the pieces towards each other so they overlap at the bicep. Continue moving them until you've removed the amount of width you calculated.

For example, if you've decided the sleeve has 2cm too much circumference, create a total 2cm overlap at the bicep.

Tape the pieces securely in place.

3. Smooth the sleeve

Check the sleeve head, hem, and underarm seams. Smooth out any areas that have become uneven, keeping the original pattern shape as a guide.

If you've removed a substantial amount, take a little extra care with the sleeve head to make sure you retain a smooth, natural curve.

What if you're making a larger adjustment?

For either a full or narrow bicep adjustment, a small change is relatively straightforward. If you're making a more substantial alteration, however, changing the width of the sleeve can affect the shape and length of the sleeve head.

If the sleeve head has become noticeably distorted, use your original pattern piece to help redraw the curve.

You may also need to adjust the corresponding armhole on the bodice if you've made a particularly large change. The sleeve and armhole need to work together, so it's important not to alter one dramatically without checking the other. If the sleeve head is very gathered, you'll have more scope to ease it into the armhole at the sewing stage than if it has little ease. Make a toile before cutting your final fabric

If you're making a significant adjustment, we'd recommend making a toile first. This is especially useful for a more involved garment such as the Manon jacket, where you don't want to discover a fitting issue after you've cut into your lovely coating fabric.

Try on the toile with the kind of layers you intend to wear underneath the finished jacket. Raise and bend your arms, move around, and generally give it a good test drive.

A coat that looks great while you're wearing a thin layer and standing still but won't let you reach for your coffee while wearing a winter sweater is not quite the forever garment we're aiming for!

A few things to check

Before cutting your fabric, check your adjusted sleeve pattern for:

• The correct amount of width at the bicep 
• A smooth sleeve head
• A straight grainline
• An even sleeve hem
• A sleeve head that still corresponds with the garment's armhole

Ready to wear?

 

Remember: The goal of a sleeve adjustment isn't necessarily to make the garment closely moulded to the shape of your arm – you need it to be comfortable when you move. Your preferred level of ease may be different from someone else's. With fitting, there's no singular magic bicep measurement that works for everyone - you do you.

Happy sewing!