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I've been getting quite a few requests lately asking how I figure out yarn requirements. Rather than responding to them each individually, I've decided to make a post about it.
There are so many different shapes and constructions for sweaters, and each one is slightly different. In this post I'll be talking about a bottom up sweater that is knit in pieces with raglan shaping. I may explain how to figure out other shapes in the future. Let me know if you're interested in anything specifically.
The first thing you'll need is a finished model sweater and a completed schematic, or at least the measurements for each piece. I like to have a schematic so I can visualize each piece, and make sure I didn't forget anything.
Below is our sample schematic. If you click on the image, it will open larger in a new window so you can follow along.
Using the schematic measurements, we'll figure out the approximate square inches of each piece. I've divided the schematic into 4 pieces that we can easily estimate. For this example I'll explain how to figure out the second-smallest size as the model garment.
The body is divided into the upper body (shown in purple) and the lower body (shown in pink).
Figuring the square inches of the upper body:
Add together the measurement at the neck edge, and the measurement at the bust.
6.5" + 18.25" = 24.75"
By adding these two numbers together, we're turning the two upper body pieces (1 front & 1 back) into a more rectangular shape. See the image below. It is much easier to figure out the square inches of a rectangle than a trapezoid.
Multiply that number by the armhole depth.
24.75" x 3.5" = 86.625"
86.625" is the square inch measurement for the upper body—both the front and back pieces.
Figuring the square inches of the lower body:
Multiply the bust measurement by the measurement from the lower edge to the armhole shaping.
18.25" x 15.25" = 278.3125" square inches each front and back.
Multiply that by 2 (1 front & 1 back) to get the total square inches for the lower body.
278.3125" x 2 = 556.625"
I don't bother removing the waist shaping because I'd rather account for more fabric than not enough.
If the bust measurement is different from the lower edge measurement, then figure it out the same way as the upper body by adding the bust and lower measurements before multiplying by the height to the armhole. Doing this accounts for the back and front, so you won't have to multiply by 2.
Figuring the square inches of the sleeve cap:
Both parts of the sleeve are figured the same way as the upper body. Whenever there is a trapezoid-like shape, add the 2 width numbers then multiply by the height.
So, for the upper sleeve add the underarm measurement to the final bind off measurement, then multiply that total by the cap height.
(13.25" + 8") x 3.75" = 79.6875" for 2 sleeve caps
Figuring the square inches of the lower sleeve:
Add the underarm measurement to the cuff measurement, then multiply by the sleeve length.
(13.25" + 9.25") x 18.25" = 410.625" for 2 lower sleeves.
Add the square inches for all the pieces together to get the total for the whole sweater.
upper body: 86.625"
lower body: 556.625"
sleeve cap: 79.6875"
lower sleeve: 410.625"
total: 1133.5625"
Figuring the yarn requirements:
Weigh your completed sweater. I tend to work in grams because that is what my scale tells me, but any weight system will do, as long as you can convert it to whatever is used on the ball-band of the yarn.
My model sweater weighs 323 grams.
Divide the weight by the square inches:
323g ÷ 1133.5625 = 0.28492383
This is the *magic number*.
Figure out the square inches for the remaining sizes, then multiply the total by the magic number. The result is the weight of each size.
1035 sq " x 0.28492383 = 295g
1252.875 x 0.28492383 = 357g
1365.375 x 0.28492383 = 389g
1511.375 x 0.28492383 = 430g
1632.3125 x 0.28492383 = 465g
1773.3125 x 0.28492383 = 505g
From there, if necessary convert the weight to the weight system used on the ball band, then add 10% to account for variations in knitting styles.
+ 10% = 324.5 (355.3, 392.7, 427.9, 473, 511.5, 555.5) grams
My ball band uses grams, and each ball is 50 grams, so I'll divide by 50 to figure out how many balls are used for each size.
6.49 (7.11, 7.85, 8.56, 9.46, 10.23, 11.11) balls.
Then I'll round it up to a whole number, and enter the information into my pattern.
7 (8, 8, 9, 10, 11, 12) balls are used for this sweater.
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