Have you ever wondered how to calculate stitch increases for top-down raglan shaping? Today, I’m going to explain the method I use, which is based on a simple simultaneous equation and quite easy to do when you know how!
First, you need the following:
|Tension||14 sts to 20 rows to 10 cm|
|Armhole height (cm)*||24 cm|
|Starting sleeve stitch number||3 sts|
|Top sleeve stitch number (without the underarm gusset)||45 sts|
And here’s how to do it:
1. Convert the armhole height from centimetres to no. of rows
2. Calculate how many stitches to increase for each sleeve – per raglan seam
3. Calculate the row interval of raglan increase
4. Put all of these numbers into a simultaneous equation
1. Convert armhole height from cm to rows
From the tension, we know that 20 rows measures 10 cm.
This means 2 rows measure 1 cm (20 rows ÷ 10 cm = 2 rows per cm).
Therefore, the number of rows in 24 cm would be:
Height in cm 24 cm x Rows per cm 2 = Height in rows 48
24 x 2 = 48 rows
2. Calculate how many stitches to increase for each sleeve per raglan seam
If we you subtract the starting sleeve stitch number from the top sleeve stitch number, (without the underarm gusset stitches), this will give you the total stitch increases for the sleeve.
(Top sleeve st without underarm gusset) minus (Starting sleeve st) = total number of increase for the sleeve
45 sts – 3 sts = 42 sts increase for the sleeve
And as there are two raglan seams for each sleeve, you need to divide the number by 2 to get the number of stitches to increase per raglan seam (fig below).
3. Calculate row interval of raglan increase
Now, you know that you need an increase of 21 sts per raglan seam over 48 rows.
This means the row intervals for the increase can be calculated as follows:
(Raglan height in rows) ÷ (St increase per raglan seam) = Theoretical row interval
48 ÷ 21 = 2.29
The number has to be a whole, even number and ideally the increase is worked on RS row (i.e. every other row or every 4 rows).
2.29 means that an increase of 2.29 rows over 48 rows will make a total increase of 21 stitches.
But in reality, this means that you increase 21 sts every 2 rows X number of times and every 4 rows Y number of times. And this is what creates a simultaneous equation.
Note: If your theoretical row interval number is less than 2, (i.e. anything up to 1.999) you would have to increase every row X times and every other row Y times etc. Whilst also making sure that in this case, X is an even number.
4. Put all numbers into a simultaneous equation
So, now you know that with an increase every 2 rows of X-times and every 4 rows, of Y-times you’ll reach the total raglan armhole height.
• You know the total number of sts to increase per raglan seam is 21.
• This means X + Y = 21.
Putting the above numbers into a basic simultaneous equation looks like this:
Equation a): (2X) + (4Y) = 48
Equation b): X + Y = 21
• Then if you multiply Equation b) by 2, you’ll get (2X) + (2Y) = 42
• Which you then subtract from Equation a) like this:
2X + 4Y = 48
2X + 2Y = 42
0 + 2Y = 6
• This shows that 2 x Y= 6
• Or it can be written as: 6 ÷ 2 = Y
• And 6 divided by 2 is 3, so Y = 3
Then, you can just replace Y with 3 in Equation b), to find the value of X:
• Equation b) is now: X + 3 = 21
• So 21 – 3 = 18
• Therefore X = 18
Understanding the numbers
Now you have X = 18 and Y = 3.
And this means that to increase from a starting sleeve stitch number of 3, to the top sleeve stitch number of 45, at underarm gusset over 48 rows, you’ll need to increase 18 times every 2 rows and 3 times every 4 rows. 3 times.
You can also use this method to calculate the raglan increase for the body, as the increase may not be the same as for the sleeves.
This is a basic method of working out the raglan increase, which I hope will help you to work out your own raglan designs!