Say you love to crochet. And say that the man you love is big and tall. If you can’t find a good sweater pattern in his size, you might sigh with relief at the thought that your relationship is safe from the Boyfriend Sweater curse. If you’re like me, though, you’ll simply start calling it a “cardigan,” roll up your sleeves, take out your tape measure and calculator, and get into some serious math.

To be fair, I’m going to tell you now that this is the first part of a series, and I don’t know how long it will be. I haven’t completed all the math for this project yet, but I did enough of it to make a start; I know what I need to do about the ribbing, the body up to the armpits, the sleeves, and the armscye. The rest will come, and when I get that far I’ll write another post. Right now, I’m going to walk you through what I’ve done so far, one step at a time.

The first step, of course, is to choose the pattern and get the approval of your victim, er, recipient. In my case, I fell in love with Shannon Mullett-Bowlsby’s “The Varsity Sweater” in the September/October 2011 issue of the “Crochet Today!” magazine. This pattern goes up to size 2x; my beloved, however, is a 3x. In this case, that’s not a bad thing; I’m going up only one size. As you’ll see in a moment, however, I’m not going up one size evenly.

The second step, even before you buy yarn, is to measure your cardigan recipient. Start with whatever measurement the pattern uses for sizing. In this case, it’s the chest measurement. The pattern’s largest chest measurement is 51 inches; my dearest’s chest measurement is a mighty 55 inches. If you work out the percentages, you’ll find that this is right around eight percent larger than the largest size. Need a little help? Here’s a percentage calculator I found online. I used the second line to find out that 55 is nearly 108 percent of 51.

This means that I’ll need to buy eight percent MORE yarn than called for by the largest pattern size. I admit to getting lazy and buying one more skein each of the main color and the contrasting color (I’m using the same color for all of the contrasting sections, rather than the two different ones the pattern uses). I might actually get away with it – this time – for various reasons, but I don’t advocate doing this. Take the yardage of your yarn, total it, and do the math. You’re much better off buying all of your yarn at once, even if it’s no-dye-lot Red Heart. I’ve seen that stuff vary a lot more than it should, and it can stand out unpleasantly in your finished project.

The third step is to make a gauge swatch. You absolutely can’t skip this step, because if you’re not getting gauge you’re going to have to do extra math to get the pattern to fit your recipient. I’ll demonstrate this in a bit with the math for the sleeves. The other reason you can’t skip this step is that you want to make sure you can find a good drape. Crocheted clothes projects, even sweaters, needn’t stand up by themselves!

In my case, I had to go up two hook sizes, from a G to an I, to get a good drape. Sadly, I could not get gauge. The pattern called for 24 stitches by 16 rows to give a swatch that is 6.5 inches long by 4 inches high. I got the length, but my height came to 4.75 inches. The length goes around the body, so at least I wouldn’t need to make any extra adjustments to the number of stitches per row (I already needed to adjust that due to my dear one’s size). For the height, however, I would need to adjust the number of rows I worked. As it turned out, the finished length of the largest size of the pattern works well for my recipient, so I simply need to apply the math to make sure I can achieve that measurement with my slightly taller rows.

This brings me to my fourth step – which is really a reiteration of your second step. You’re going to need to measure more than just the chest size of your pattern. Sweater patterns typically come with a schematic, which is a drawing/diagram that shows you how your sweater looks after the knitting or crocheting is finished, but before all the pieces have been assembled. It also lists measurements for the various sections right next to the relevant areas. Measure your recipient in these corresponding areas. They will probably include the length of the full garment, back width, shoulder width, size of armscye (that’s the armhole on the body of the sweater), sleeve length, sleeve width, and circumference of the wrist.

I got a couple of surprises here. First, my beloved’s armscye is two inches larger than the largest size of the pattern. I figure I can accommodate this by making the entire pattern from the armpit up about one inch longer. The fact that my rows are already a bit taller than they need to be should help me here. But I’m saving that math for later, because right now I want to talk about sleeves.

Just because a man is tall, big, and wears a large size, doesn’t mean he has long arms. It turned out my recipient’s arm length is the same as that given for the LARGE size of this pattern – NOT the 2x size. That was my second surprise. Can you imagine what would have happened if I’d sized the entire pattern up uniformly, without taking this possibility into consideration? The sleeves would have gone well past his hands! Likewise, his wrist circumference is 10 inches, not the 11 inches used on the sleeves of the larger sizes.

Here is the challenge though: I need to fit this size large sleeve onto an armscye that is two inches LARGER than the 2x armscye. Here, we’re going to get into some actual, intense math.

I need to make this sleeve 24 inches at its widest point. I can get 6.5 inches in 24 stitches. Twenty-four inches, divided by 6.5 (you’ll see why I’m doing this in a minute) is about 3.7. Take 3.7 and multiply by 24 (for the number of stitches in 6.5 inches) and you get 88.6 – rounded up to 89. That’s the number of stitches I need to have in the sleeve at its widest point.

With 89 stitches as my goal, I start by looking at the bottom of my sleeve. The wrist starts with 37 stitches. The pattern already features rows of increases, of course, and these add two stitches every time. Twenty-six increase rows will get me to my target of 89 stitches.

Here’s the next question: how frequently should I work an increase row? Well, the large sleeve pattern spreads increases over 73 rows, before decreasing back to just a few stitches. We know that 16 rows in the pattern’s gauge equals four inches, so four rows equals one inch – so 73 rows equals 18.25 inches. But remember, I couldn’t get gauge in this dimension; my 16 rows came to 4.75 inches. That’s nearly nineteen percent bigger!

Once again, math comes to the rescue. But this is pretty darn complicated math. We know that 73 rows is too many, given my gauge. We need to find a figure that is eighteen percent LESS (smaller) than 73. I went with eighteen percent because the numbers work out better, and it won’t substantially affect the fit. Anyway, how do we find this number?

We go back to what we learned about percentages in grade school. They can also be written as decimals – and if you want to find out percentages of something, you can multiply by these decimals. If one hundred percent is 1.00, then subtracting 18 percent gives us a figure of 0.82. We want a number that is 73 less 18 percent, so we multiply 73 by 0.82. The figure we get, rounded up, is 60. So we need to spread twenty-six increase rows evenly over 60 rows. That’s almost, but not quite, an increase row every other row.

How about the decreases for the sleeve cap? The large size sleeve allows for 24 rows of decreases, decreasing two stitches each row to take it down to a single stitch. But the 2x size decreases to three stitches, so I figure if I need to, I can leave three stitches after all of the decreasing is done. Still, here it gets a little challenging. Remember my stitch height problem? The pattern wants this decreasing section to measure six inches from start to finish. With my gauge issue, that same 24 rows will be more than an inch longer than it should be. That’s just enough of a difference to be annoying when you wear it.

So let’s take those 24 rows and multiply by 0.82. We get 20 rows. And here we run into a problem: how do you decrease 89 stitches to, at most, three stitches over the course of 20 rows? You can’t do it by just decreasing two stitches every row. Here I’m going to have to take a deep breath and hope that a serious rewrite will still allow the pattern to fit. I’m going to have to decrease at least four stitches every row. And you’d better believe I’ll be pinning the sleeve and trying it on my big and tall man to make sure it fits!

I hope all that was pretty clear. What changes have you made to knitting and/or crochet patterns to make sure they’ll fit?