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How to do a bicep adjustment

Have you ever made a garment that fits perfectly through the bodice but feels too tight around your arms?

It sounds like something pretty minor, but wearing clothes that don't fit properly is not only restrictive (try to raise your arms above your head, for example!), but it can also be pretty uncomfortable.

This fit issue happens quite often and can sometimes trick you into thinking that the back or bodice of the garment needs adjusting, when in reality you need to adjust the sleeves.

The beauty of bicep adjustments

Making adjustments to patterns can feel a little overwhelming, but a bicep adjustment is a great place to start.

What I love about this particular adjustment is that the general shape of the pattern piece remains the same and we only add the extra fabric EXACTLY where it's needed.

By adding fabric in the centre of the sleeve, we're not changing the measurement of the sleeve head, or the length of the sleeve. Nothing else needs to be adjusted. Pretty cool, huh?!

How to do a bicep adjustment

But before doing any pattern alteration, we need to be sure that it's the right alteration to do. Here's what I recommend.

Make a mock-up

Making a toile (or muslin) of the area that is causing problems is a great way to figure out what the problem is, without wasting your good fabric. I like to make a mock-up of the entire garment with both sleeves inserted.

Signs that you need to do a bicep adjustment

Try on your toile and stand in front of a mirror. Wrap your arms around yourself like you're giving yourself a hug. Have a look at what's happening with the garment when you do this.

You will be able to tell if the sleeves are too tight through the bicep if you notice pull lines underneath your arms from your bicep towards your back.

Or, if your shoulder seam is being pulled down and not sitting at your shoulder joint.

Do a mock-up test

Using your scissors cut a slit in both sleeves at the middle of the bicep starting approximately 2" above your elbow and stopping 2" below your shoulder.

Once cut, the fabric will spread apart to accommodate your bicep. You should no longer feel the pull through your back when you hug yourself and the shoulder seam will no longer be pulled downward.

When relaxed, with your arms by your side (you might need someone to help you do this!) measure where the fabric has spread at the slit at the widest point.

This is the amount we need to add into pattern with the bicep adjustment.

Hot tip!

If you cut the slits at your biceps and the fabric does not spread it may mean the fit issue is actually through your back and you should consider doing a broad back adjustment, not a bicep adjustment.

How to do a bicep adjustment

Once you know exactly how much you need to adjust your pattern by we need to go back to the pattern and make the appropriate alternations.

To begin, trace the sleeve pattern onto pattern paper, interfacing or just regular paper. (We don't want to make changes to the original pattern because then we won't have the pattern anymore!)

I recommend watching this video tutorial for how I do it, but I've also included step-by-step instructions below.

Step 1 - Mark up your pattern piece

Mark up your sleeve pattern piece.

Using a ruler, draw a straight line from the centre of the sleeve cap to the centre of the sleeve hem.

Then, draw another straight line intersecting this line, from the opposite sides of the sleeve at the points where the seam meets under your arm.

Step 2 - Cut along the lines, leaving hinges at the ends

Cut along the lines of the sleeve pattern, leaving hinges at each end.

Using a rotary cutter and a ruler, cut along the lines leaving a small hinge at each end (top and bottom of the sleeve and at each point) so that the pattern piece stays together. So, this means that you don't cut all the way across - you're actually cutting a slit in the pattern, along the line.

I really recommend watching the video for this!

Step 3 - Adjust the pattern piece by pulling it out at the sides

Move the sleeve out until you have added in what you need.

We now want to adjust the sleeve pattern piece by moving the edges out. This creates more room in the centre of the sleeve, making it larger. The cut pieces will overlap slightly as you pull out the corners.

Adjust the pattern piece to create a space in the centre that matches the measurement you took when you were testing with the mock-up. Your measurement will only be the gap where the paper is overlapping, as shown in picture above.

Use tape to hold the new shape in place.

Step 4 - Redraw the sleeve head, if necessary

Redraw the curve of the sleeve head, if necessary.

If you're adding more than an inch (2.5cm+) to a sleeve pattern, you will probably find that the curve of the sleeve head starts to flatten out. Redrawing the sleeve head curve can be done easily with a French curve, like on my Fashion Multi Tool.

Just slide some paper underneath and trace around the straight edges of the pattern piece. Align the French curve top so that it creates a nice smooth curve in the sleeve head. This might take a bit of fiddling, but when you're happy with it draw it in.

Step 5 - Measure to check

Measure the length of the sleeve head and compare it to the armhole measurement. They should be the same or very close. If you're working with woven fabric the sleeve can be slightly bigger than the armhole, but not the other way around.

If you end up having to add more than 3cm for your bicep adjustment, you may find that you need to slightly gather your sleeve head to help it fit into the armhole (armscye).

And you're done!

What do you think? Keen to give this adjustment a go? Let me know in the comments, or feel free to ask a question too!


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Welcome to Sew To Grow!
Our mission is to help you build a perfectly fitted handmade wardrobe, so when someone asks where you got your fabulous frock you can confidently say 'I made it!'. To help you on your sewing journey, here you'll find a range of tutorials about sewing techniques, garment fitting, notions and tools, fabric and more!

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