Armhole Knitting. How to Shape & Knit – Always Perfect Result!

armhole shaping

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Here you are… Knitting first time sweater with armholes for set-in sleeves? And you are not familiar with armhole knitting? Or how to measure arm holes?

This tutorial is for you. Many illustrations. Easy math.

Starts with some theory (oh, well, can’t escape that) and after I will show you real world example and we get through this together!

There are several ways to work armholes, depending on the shape you want. Most involve a mixture of casting off stitches for the underarm, and decreasing stitches towards the shoulder.

I dedicate this tutorial to set-in sleeve armhole.

Also, I have a tutorial how to knit perfect set-in sleeve cap

After reading and watching all the tutorial you will learn how to attach a sleeve to armhole as well.

How to measure arm holes in knitting

Armhole – measure in a straight line at the point where sleeve joins body at the shoulder to where the sleeve meets the body at the underarm. And you are not familiar with armhole knitting?

knitting good

There is a standard formula for calculating armhole length.

Armhole (cm) = BUST/6 + 3.5 to 6 cm.


Armhole (in) = BUST/6 + 1.37 to 2.36in. 

Explanation. Measure Bust size and divide by 6. Then  add 3.5 to 6 cm (or corresponding inches) depending on your size.

If you struggle to find the right measurement there is a standard armhole measurement table as reference. 

From here armhole doesn’t change in size2620+4249.45

How many stitches to reduce for armholes?

First, we determine how many stitches we need to reduce. The width of the armhole usually is 4-6 cm (5/32″-15/64″). A-B in the drawing below. If you are size XS – S, most likely you will have 4cm. Size M-L-XL more likely 5-6 cm.

Second, there is another easy way to determine how many stitches to reduce. Put a stick under each armpit. Measure distance between the sticks. That is how many cm (or Inches) you need to get after decreases. Sticks have to be parallel! Ask someone to measure it properly!

Let’s say I have 45cm wide piece of knitting at the underarms. Distance between sticks is 35 cm. I need to reduce 10 stitches (5 cm) on each side. 

Third, get your favorite piece of garment and measure width.

How to measure an armhole
How many stitches need to be decreased to shape an armhole.
Armscye knitting for set in sleeve
1. Armhole


I exaggerate underarm in the picture in order to show how to divide stitches. Usually it is not so wide compared to shoulder point.

We calculate how many stitches are in 1 cm (or inch). To do this, you just need to know your gauge. My gauge is 2 stitches wide and 3.1 stitches in height per 1 cm.

I am size M, so I will reduce 10 stitches (5cm) from each side.

Divide the resulting number of stitches into 3 parts. I-II-III parts in the picture.

If this number is not divisible into a whole number, then add remainder to the first (I) part of the stitches, which is closer to the Underarm (Point B).

We get 3 blocks of stitches.

1. The first part (I) of the stitches are closed in one go.

2. The second part (II) of the stitches decrease by 1 at the beginning and end of the knit row. Purl rows are without decreases. Basically, decrease every 2nd row.

3. The third part (III) of the stitches we reduce by 1 stitch every 2nd knit row. Basically, every 4th row.

Example: the number of stitches that are reduced for the armhole is 10.

Divide into 3 parts: 4, 3 and 3 stitches.

Part I. Bind of the first 4 stitches.

Part II . Decrease 3 times 1 stitch every 2nd row. 

Part III:  Decrease 3 times 1 stitch every 4th row.

Note. Decreases are made in the beginning of the Knit and Purl rows accordingly. Technically, you can’t bind off at the end of the row.  

Row 1. Knit row. Bind off 4 stitches. Knit to the end of the row. Turn. Now you are on a purl side.

Row 2. Purl row. Bind off another 4 stitches. Purl to the end. Turn.

Row 3. Knit row. Decrease 1 stitch. Knit to the end. Turn.

Row 4. Purl row. Decrease 1 stitch. Purl to the end. Turn.

Row 5. Knit row. Knit all stitches without decreases. Turn.

Row 6. Purl Row. Decrease 1 stitch. Purl to the end. Turn. Etc.

Armhole knitting schema

Get your shoulder point in the right place.

It is important to locate the shoulder point anatomically right. In classic set-in sleeve construction, shoulder point should match shoulder joint. That is important in armhole knitting because it can change the look drastically.

knitting shoulder point right

How to make arm holes when knitting in the round?

You can knit bodice in the round until you need to start armholes. Armholes are openings. You need to split body into 2 equal parts (back and front) and knit flat each part.

Although, there is knitting technique called steeking as in Fair Isle knitting, where you knit all in one piece and cut the openings in the end, but it works only with straight openings. You would not want to use it for armhole shaping as in this tutorial.

Is it possible to knit arm holes using circular needles? Yes, you can use circular needles for back and front knitting, but it still will be flat knitting, not in the round.


How to get smooth decrease edge and get away from ugly steps.

Solution is very simple. When you are knitting to the end of the row, do not knit (purl) the last stitch. Turn your work and the last stitch becomes first one, slip the next stitch and pass first stitch over (psso). 

Decrease armhole without steps knitting

After decreasing, you knit the rest of the armhole straight until you reach desired size (red line on the picture 1. armhole). 

There is another little tweak you can make.

If you look at the armhole picture 1. armhole, you can see 1cm wide increase on the top (green). You can increase a few stitches to make upper part slightly wider. 

But you don’t have to, specially if you are knitting ribbing or complicated pattern where it would be difficult to add a few stitches without headache. 

Shaping armholes on back in knitting

Usually we knit front and back the same. But for tailor-made fitting, we can decrease a few stitches less in the armhole, it will make back slightly wider.  

How to bind off more than 15  stitches for armhole?

Previous example is perfect for reducing up to 15 stitches. If you need to reduce more,  you need to divide all stitches into 4 groups.

Example: We have 25 stitches.

Divide into 4 parts: 7 – 6 – 6 – 6. (remainder is added to the first part)

Part I. Bind of the first 7 stitches.

Part II. Divide into groups of 3 stitches. Reduce by 3 stitches every 2nd row.

Part III. Divide into groups of 2 stitches. Reduce by 2 stitches every 2nd row.

Part IV. Divide into 1. Reduce by 1 every 4th row.

reduce large amount of stitches


You don’t need to be an expert to manage knitting armholes. It is understanding simple math and proportion.

Knit once in plain stockinette, and you will get the understanding. And later, you will be able you calculate armhole yourself for more complicated patterns.

This guide suits you as a reference.

Do not forget to look at the knitting sleeve cap tutorial.

You may like:

Round Neckline Shaping

Knit Short Row Neck Hole

armhole knitting tutorial

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