Understanding the Sleeve Part 3: The Triangle

There are four parts to this article on Understanding the Sleeve and they follow on from each other . In order to get a well-fitting sleeve, you need to get the measurements of the triangle which underpins the curve correct.  So let’s strip away the curve and look at just the triangle.   Since it’s a triangle, there are of course three sides, but the height of the triangle – called the Cap Height, also plays a part.

The Front & Back Armhole Measurements

When creating a sleeve, we make it to fit a Bodice Block. The sleeve you would be making on this website is to fit the Bodice Block you have made.  you can therefore measure the back and front armholes, and plug this measurement into the triangle above to make the sleeve. In order to get the extra ease you need in the sleeve cap, you also need to add 0.25-inches to both the back and front armhole measurements.  This ease that is added to the  straight lines, plus the additional length that is added by the curve that is built around this straight line, ends up giving us the ease we need to sew the sleeve cap onto the armhole.  This ease is usually between 1.25-1.75-inches.  This means the sleeve cap curve measures 1.25 – 1.75-inches more than the front and back armholes added together. So looking at the triangle again and applying basic math, it should be obvious that (given we have the armhole measurements, and we want to use those measurements) we can either set the Bicep measurement or the Cap Height.  If we set both the Bicep and the Cap Height, we may end up incorrect measurements for the back and front armhole. If this is not obvious to you, there are some images below to clarify it.

 Examples: Cap Height/Bicep Relationship

If we change the Bicep – for example, increase it by 1 inch, and we leave the Cap Height the same, we will be increasing the armhole measurements: If we increase the Bicep but reduce the Cap Height, the armhole measurements remain the same. Likewise, if we change the Cap Height – for example, increase it by 1 inch – and we leave the bicep the same, we have to increase the armhole measurements. Likewise, if we change the Cap Height – for example, increase it by 1 inch – and we also increase the bicep, we have to increase the armhole measurements.

So what does this mean?  Bicep or Cap Height?

It just so happens that with the Standard Figure, that the Bicep/Cap Height relationship works out well.  Meaning that if you set the Cap Height, you end up with the correct bicep measurement (including 2 inches ease).  If you set the Bicep, you end up with the correct Cap Height.  This ideal relationship between the two means your armhole measurements remain correct,and you end up with the ideal fitted sleeve block.  The ideal fitted sleeve block is minimal ease in the sleeve cap and minimal ease in the bicep. If you don’t have a standard figure, and by that I mean:
  • your bicep is proportionally larger for your size
  • you need more ease in the bicep than 2-inches*
then the (bad?) news is that in your case, the ideal Fitted Sleeve is not quite so easy.

Bicep & Cap Height: The Problem

The ease that is added to the bicep isn’t just ease for the bicep.  It also includes ease for the upper arm.  If you have larger than normal upper arms, and/or forwards sloping shoulders (and maybe other fitting issues), you may need up to 4-inches ease at your bicep level. The contradiction here is:  if I need 4 inches ease in the bicep to make the sleeve wearable, that really is still minimal wearing ease.  However, for a Fitted Sleeve Block, adding 4 inches ease to the bicep, and using your actual Cap Height means you will probably end up having excess ease in the Sleeve Cap.  Either way you don’t have the IDEAL amount of minimum ease.


In the image below, the brown sleeve is made with my bicep measurement (plus 2 inches ease) and my cap height measurement.  The result is a sleeve with minimal ease in the bicep and minimal ease in the sleeve cap. If I stand with my hands by my side it seems to fit; there is enough ease in the bicep for the actual bicep.   However, when I reach my arms forward it pulls from the mid back of the sleeve to the front armhole side seam point.  The constriction borders on painful, but at the minimum is extremely uncomfortable. There isn’t enough ease for my upper arm to reach forward, and in order to fix this, I need to add extra ease to the bicep. If I increase the bicep ease to 4-inches, I get some extra ease in the place where it pulls; this sleeve will make a comfortable sleeve that I can wear.  It also has the minimum amount of ease in the sleeve cap, so there won’t be gathers and tucks in the sleeve cap.  However, it’s not using my Cap Height and it flares out a bit from the arm instead of following the contours. Is it still a fitted sleeve?  Well, that’s the question….. how fitted does a Fitted Sleeve have to be to be a Fitted Sleeve? In the image below, I have the 4-inches ease in the Bicep AND kept my Cap Height.  As you can see, I have even more ease for my forward-stretch, but my sleeve cap has now increased by 2-inches.  That is 2-inches more than the minimum amount needed to sew the sleeve into the armhole. In this case my options are:
  • live with the some gathers in the sleeve cap. (Do I care I can’t have the ideal fitted sleeve cap?)
  • put in a dart or two to remove the excess ease
  • put a seam line in, so it is a two-piece sleeve, rather than a one-piece sleeves, and remove the excess in the seam line
Neither is ideal, but then I don’t have the Standard Figure. Which of the above two should I use for my Sleeve Block?  What does it mean that regardless of which of the two options above I use, I don’t have the ideal ease in the sleeve and sleeve cap? Continued in Part 4: The Bicep or the Cap Height?

3 Responses

  1. Thank you for the detailed information that’s not a video. I’m old school and prefer illustrations and words I can refer to while I’m drafting.
    I’m creating four bespoke men’s sport coats for my local theater. I purchased a pattern and altered it to fit each guy, but have learned today that the sleeve in the original patter isn’t true. It’s been 41 years since I got my design degree and close to 15 years since I’ve had the chance to tailor clothes so my brain is a little rusty on sleeve alterations. I greatly appreciate your sharing your knowledge in an easy to understand manner.

  2. Hello. The only part I’m not %100 seeing which could be me… Is how I would collect these measurements for the triangle on a person without a pattern. Is it top center of shoulder to the center arm pit front and then again just to across the back ?Then top of the shoulder to the start of the bicep for the cap? Thanks.

    1. The sleeve is drafted to fit a bodice block, so you need a bodice block with the measurements of the armhole as a starting point. I have a video with step-by-step instructions for drafting the sleeve, but again, you need a bodice block first.

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