How to shape armholes in knitting

Learn how to adapt sleeveheads and armholes on three main sweater shapes for a perfect fit with Jen Arnall-Culliford's masterclass

How do I shape armholes in knitting

One of the best things about knitting your own sweaters is being able to adjust them to get the best possible fit. Whether you have a long torso, broad shoulders or very short arms, you can make hand-knitted garments work perfectly for your body. In this Masterclass, we will work through how to adjust armhole depth for three of the most common sweater constructions. This is one of the more complex adjustments you can make to a sweater, since it means you need to adapt both the armholes on the body and the sleeveheads, ensuring they will still fit together correctly.

How to shape armholes in knitting patterns
Drop-shoulder styles are the easiest to adapt. ‘Aubusson’ from The Knitter issue 92.

The most straightforward construction is the drop-shoulder, so adjusting the armhole depths on this type of sweater or cardigan isn’t too complicated. There is no shaping involved in the armhole; you simply place a marker at the side of the body to show the start of the armhole, and then work until you have the desired depth, before shaping shoulders and neck, or simply casting off. You will then need to adjust your sleeves to match.

Drop-shoulder sleeves have no shaping at the sleevehead. Once the desired top arm circumference is reached, and the sleeve is the correct length, all stitches are cast off. Top arm circumference is always twice the armhole depth.

Simple adjustment

The simplest way to do this is to look at your pattern and see whether another size has the armhole depth you desire. If so, you can simply work the sleeves according to the instructions for that size (adjusting for length if you wish), and then change the depth of the armhole on the body.

More complex adjustment

If none of the pattern sizes will give you the desired armhole depth, you will need to re-calculate your sleeve shaping to give a sleeve top to match your new armhole.


Step 1

In our example, we wish to make a sleeve to fit an armhole depth of 23cm (it was previously 20cm).

2 x Armhole depth = Width of top of sleeve

The top of the sleeve therefore needs to measure 46cm (2 x 23cm). See diagram 1.

How to shape armholes in knitting Figure 1

Multiply your stitch tension per cm by the desired width to calculate how many sts you need at the top of the sleeve.

Width of top of sleeve x sts per cm = Stitches required at top of sleeve

46cm x 2.2 sts per cm = 101.2 sts

Round your answer to the nearest odd or even number (to match whether the sleeve started as an odd or even number). In this example we will round to 102 sts.


Step 2

Starting with the original cuff instructions for your bust size, you will then need to space out your increases to fit within your sleeve length.

E.g. The cuff starts with 50 sts and you wish to increase to 102 sts. The sleeve needs to be 48cm long in total, with 5cm of cuff at the start.

Firstly calculate how many increase rows you will need. You intend to increase 1 stitch at each end of the increase rows (2 sts increased).

(Final stitches – Start stitches) ÷ 2 = Number of increase rows required.

In our example, (102-50) ÷ 2 = 26 increase rows.


Step 3

Then space the increase rows regularly in the remaining length after the cuff.

Total sleeve length – Cuff length = Length available for increases

48cm – 5cm = 43cm

Length available for increases ÷ Number of increase rows = How often to work an increase row

43cm ÷ 26 increase rows = 1.6cm per increase row (always round down, since rounding up could leave you with a sleeve that’s too long)

In this example I’d suggest working an increase row every 1.5cm (between 4 and 5 rows). Once the increases are complete, work straight until you reach the desired sleeve length, then cast off all stitches.



Knitting masterclass drop-shoulder sleeves
Drop-shoulder sleeves have no shaping at the sleevehead. ‘Little Paisley’ from The Knitter, issue 95.

Gauge information

You will need to calculate the stitch and row gauges per centimetre in order to do all of the more complex adjustments in this article.

Take the number of stitches (or rows) and divide it by the number of cm given. Round it to one decimal place.

E.g. 22 sts and 30 rows to 10cm

Stitch tension per cm = 22 ÷ 10 = 2.2 sts per cm

Row tension per cm = 30 ÷ 10 = 3.0 rows per cm

Set-in sleeve sweaters

This is the most common construction for knitted garments. The shaping of both armhole and sleevehead reduces excess fabric at the underarms and gives a flattering, fitted shape. Unfortunately, this makes altering armhole depths slightly more complicated, since the shaping on the sleevehead then needs to be completely adjusted to fit into the new armhole. The total circumference of the armhole needs to match the length of the total outline of the sleevehead, so that the sleevehead can be set in without puckering or stretching the fabric. There are many possible methods to ensure that this relationship is correct. Below you will find one method explained in detail.

Simple adjustment

Providing that you aren’t looking to make a significant change to the armhole depth (a cm either way would be fine), you may be able to combine your chosen bust size instructions with the armhole depth from a neighbouring size (one smaller or one larger; we will call this the armhole size).

Keep the neck and shoulder shaping as specified in your chosen bust size, but work the straight part of the armhole longer or shorter, according to the armhole size instructions. Then, when you make the sleeve, follow the sleeve instructions for the armhole size. When you seam the sleevehead, you will find that the underarm cast-offs may not match exactly, but given the stretchy nature of knitwear, it shouldn’t cause a significant problem.

For example, in the Cinzia pattern in Issue 96 of The Knitter, if you wanted a finished bust size of 104cm, then the existing armhole depth is 18cm and you could use the armhole depth and sleeves from either one size smaller or larger (thus giving an armhole depth of 17-20cm). The tension for this pattern is 22 sts and 28 rows to 10cm.

How do I shape armholes in knitting
Adjusting set-in sleeves such as on this ‘Cinzia’ design requires some maths. Pattern from The Knitter  issue 96.

More complex adjustment

If you want to make a larger adjustment to the armhole depth of your sweater, you will need to rework the shaping at the top of the sleevehead.

In this example, I shall assume that you are happy with the existing top arm circumference of the sleeve. Work your front and back, according to the instructions for your bust size (104cm). When instructed to work the straight section of the armhole (after the initial armhole shaping), increase or decrease the depth as required.

In our example we are looking to make a bust size of 104cm and to adjust the armhole depth to 21cm (it was previously 18cm), so you would work straight to 61cm instead of 58cm. Complete the neck and shoulder shaping as instructed for your bust size.

For a standard, neatly fitted set-in sleeve sweater, the sleevehead will have the same initial cast-off sts as used on the body at the underarm. The final sleevehead cast-off will correspond to approximately 7-10cm of stitches, depending on your size (it may be up to 12-13cm for men’s sizes or more relaxed fit women’s sizes).

Between the initial sleevehead cast-offs and the final sleevehead cast-off, you will work decrease rows (usually a combination of decreasing at each end of every row, alternate rows, and possibly on 4th rows).

The total number of rows worked in the sleevehead shaping will correspond to a sleevehead depth of approximately two-thirds of the armhole depth (with an extra centimetre or so added for ease).

This rule of thumb holds only for standard, neatly fitting set-in sleeve constructions. For particularly narrow or wide sleeves, or sleeves with unusual design features, the sleevehead shaping will need to be calculated from first principles.

Example 1 (Cinzia):

First, identify how many stitches you have on your sleeve after the initial sleevehead cast-offs. E.g. Widest part of sleeve has 85 sts. You then cast off 9 sts at the start of the next 2 rows, leaving 67 sts.

Second, identify how many stitches are remaining at the final sleevehead cast-off. E.g. Cast off remaining 25 sts.

Calculate how many decrease rows you need. You intend to decrease 1 st at each end of the decrease rows (2 sts decreased).

(Stitches after initial cast-offs – Final sleevehead sts) ÷ 2 = Number of decrease rows required

(67-25) ÷ 2 = 21 decrease rows required

Work out how deep you want the sleevehead to be (in the original pattern it was 18cm, we want to change it to 21cm):

(Armhole depth x ⅔) + 1cm = Sleevehead depth

(21 x ⅔) + 1cm = 15cm

Calculate how many rows of sleevehead shaping you need to work in order to give this sleevehead depth:

Sleevehead depth x rows per cm = Number of rows in sleevehead shaping

15cm x 2.8 rows per cm = 42 rows of sleevehead shaping

You need to work a total of 42 rows, and 21 of these rows need to be increase rows. The remaining 21 rows will be WS rows with no shaping. This is a simple adjustment to make since all you need to do is to decrease at each end of the row on 21 alternate rows. This will give a total of 42 rows of sleevehead shaping, and should fit the new armhole depth nicely.

Example 2 (see diagram 2):

Here is another worked example where the shaping doesn’t work out quite so neatly. The original pattern has an armhole depth of 19.5cm and we want to change it to 21.5cm. The widest part of the sleeve has 82 sts and you cast off 6 sts at the start of the next 2 rows, leaving 70 sts. There are 16 sts remaining for the final cast-off row. The tension for this design is 22 sts and 30 rows to 10cm.

How to shape armholes in knitting step 2

Calculate how many decrease rows you need.

(Stitches after initial cast-offs – Final sleevehead sts) ÷ 2 = Number of decrease rows required

(70-16) ÷ 2 = 27 decrease rows required

Work out how deep you want the sleevehead to be (in the original pattern it was 14cm):

(Armhole depth x ⅔) + 1cm = Sleevehead depth

(21.5 x ⅔) + 1cm = 15.3cm

Calculate how many rows of sleevehead shaping you need to work in order to give this sleevehead depth:

Sleevehead depth x rows per cm = Number of rows in sleevehead shaping

15.3cm x 3.0 rows per cm = 46 rows of sleevehead shaping

You need to work a total of 46 rows, and 27 of these rows need to be increase rows. The remaining 19 rows will be WS rows with no shaping.

The number of remaining rows tells you how many alternate row decreases to work (since each RS decrease row will be worked with a WS plain row in between). This accounts for 38 of the rows, leaving 8 rows where decreases will be worked on every row.

In order to achieve a pleasing sleevehead curve, it is usual to split the most frequent decreases (here it is the every row decreases) between the start and the end of the sleevehead shaping.

So for this example, the sleevehead shaping would now look something like this:

Cast off 6 sts at start of next 2 rows. 70 sts.

Dec 1 st at each end of next 5 rows. 60 sts.

Dec 1 st at each end of 19 following alternate rows. 22 sts.

Dec 1 st at each end of next 3 rows. 16 sts.

Cast off all sts.

Total rows worked = 5 + (19 x 2) + 3 = 46 rows

How to measure armhole depth

One way to find the right armhole depth for you is to measure an existing sweater that fits you well. Measure from the top of the sleeve down to a point level with where the armhole begins. As this may differ from garment to garment, choose a sweater with a similar sleeve shaping to that of the pattern you want to adapt.

How to measure armholes in knitting

Seamless yoke sweaters

In a seamless yoke sweater, the body and sleeves are worked as tubes, before being joined at the yoke. Stitches are left on holders for the underarms (to be grafted later), and you then knit around the left sleeve, front, right sleeve and back (or starting at another point, but working in the same order). The yoke stitches are then gradually decreased until you’ve worked sufficient depth of yoke, and you’re left with your desired neck circumference.

Simple adjustment

In order to increase the armhole depth, you simply need to increase the yoke depth (see diagram 3). This is usually straightforward, since you just need to work more rounds between each of the shaping sections.

How to shape armholes in knitting Figure 3

Calculate how many extra rounds you need:

Extra yoke depth required x rounds per cm = Extra yoke rounds required

2cm extra yoke depth x 3.0 rounds per cm = 6 extra yoke rounds

Spread these rounds out between the shaping rounds, adding most of them in the first half of the yoke.

Knitting armholes masterclass back
Adjusting yoked designs is usually straightforward. “Hosten” pattern from The Knitter issue 89

Adjusting to fit

Slipping your stitches onto waste yarn in order to try on sections as you go can be extremely helpful, as can basting sections together for a quick try before you commit to neatly stitching seams at the end of a project.

The beauty of knitting is that if it isn’t right first time, you can rip it back and try again. Whilst it’s frustrating to have to reknit a section of a garment, it is almost always worth the extra effort to end up with a sweater that fits really well.