Wrong. Yes, some parts of your body get bigger when you get wider. You'll definitely need more room in the torso, armholes, sleeves, even the back neck. But on a plus-size sweater, especially at larger sizes, your sleeve length may actually get shorter.
That's right. You may have experienced this problem if you've ever worn a man's shirt or sweater. Let's say you bought a 3x (or 10x for that matter) tee shirt. You're thrilled because it covers all your vital bits. But the sleeves go past your elbows and beyond. Why is this?
Drop sleeve shirts and sweaters are comprised of four rectangles: two for the body and two for the sleeves. This is probably the easiest garment to make because it doesn't require any shaping for the sleeves or body, although you often have some shaping for the neckline.
Smaller-sized tees are designed to be between 45- and 55-inches wide from sleeve to sleeve. This is a fixed width, right? Even if you get wider, the length between your elbows does not change. As I got fatter, my arms never got longer; they only got chubbier.
Unfortunately, clothing manufacturers and most knitwear designers think that to upsize a garment, all you have to do is make something exponentially larger.
WRONG. What you end up with when you make a garment exponentially larger is way-too-long sleeves and mishapen, ill-fitting necklines. Again, your arms don't get longer when you get bigger. They stay the same, which means that any exponentially larger garment will not fit you properly.
Therefore, if you want to make a larger drop-sleeve garment, you actually need to make your sleeves shorter. When you expand the width of the sweater, you then need to adjust the length of the sleeves.
So, the next time you're knitting a drop-sleeve or modified drop-sleeve sweater, check your sleeve length. Actually, the next time you're knitting anything, check your sleeve length! I've made more than one sweater with arms that were way too long.
Another caveat: if you make sweaters with Sweater Wizard, you MUST adjust the sleeve lengths. This invaluable software makes makes it easy to knit ample sweaters, but the sleeves are exponentially sized. If you don't watch out, you'll end up making sleeves fit for Kareem Abdul-Jabbar!