Most garment knitters will need to adjust the shaping in a pattern at some point. This might be needed are when you need to lengthen or shorten a shaped portion of a garment, such as a sleeve. Or you may get the stitch gauge for the pattern, but your row gauge may be quite different from the specified gauge.
Pattern designers have some fairly complicated spreadsheet formulas to calculate shaping in sweaters, and you’ll often see shaping, most often on a sleeve, that happens at two different rates. This is done in order to make the shaping as smooth and consistent as possible. If the shaping happens too quickly, you may end up with a sleeve that looks more like a turkey leg.
(Note: Raglan shaping is more complicated because it involves more than one piece of the garment, so I won’t be discussing that here. The same principles apply, but you may require more trial and error to get the correct shaping.)
The reason designers use spreadsheets, though, is to make it more efficient for writing multiple sizes. Since you are only working one size, you can use some fairly simple math, and a bit of trial and error, to adjust for your gauge or sizing.
Basic Shaping Math
Let’s look at shaping math using sleeves as our example. The first thing you need to know is how many rows you have available for shaping. To determine this, you need to multiply your desired length by your row gauge. Typically, on a sleeve you won’t be doing any shaping in the ribbing or cuff section, and it’s best to leave about an inch between the shaping and the armhole, so you’ll want to take that into account by subtracting those from the length for shaping. So your calculation will look like this:
# rows for shaping = (Sleeve length – cuff length – 1 inch) x gauge (rows/ inch)
Now, here is the basic formula for shaping:
Rate of shaping = # rows for shaping / # of shaping rows needed
This is the basic slope formula you learned in math class: slope equals rise over run. In this case, slope is the number of shaping rows needed. The ‘rise’ is the number of rows you have available for shaping, or in other words the length of the shaping. The ‘run’ is the number of stitches you need to remove divided by the number of stitches added or removed in each shaping row (typically 2 stitches for a sleeve).
Simple shaping
If your pattern has only a single rate of shaping, you can use the formula above to calculate a new rate of shaping. You may have a few rows left over – on a sleeve you can work those extra rows at either the cuff, the small straight “work until” section between the shaping and the underarm, or split them between the two.
More complex shaping
If your sweater has more complex shaping, for example:
“Rep Inc row every 6 rows 20 (18, 18, 18, 16, 8, 6, 10, 3) more times, then every 8 rows 1 (3, 3, 3, 5, 11, 13, 10, 16) times”
start by using the simple shaping formula above. A quick and dirty trick is to check how many rows it would take to do all the shaping using the lower number of rows (if you need to shorten the sleeve), or at the higher number of rows (if you need to lengthen the sleeve). If that doesn’t leave you with too many rows left over, you’re good to go.
If using a single shaping rate doesn’t work for your situation, add a couple of extra rows in between just a few of the repeats.
Sleeve Shaping Examples
Is this confusing? Here’s are a couple of examples:
Example 1: Different Row Gauge
The sample instructions above are from my Composure Cardigan. Let’s say I’m making the 3rd size, with a 40 ½ inch chest circumference, and my row gauge is 32 rows/ 4 inches. The sleeve length (from the schematic) is 19 inches, and according to the pattern I need to work 22 shaping rows (to remove 44 stitches).
First, I calculate the number of rows available. The shaping starts after working 2 inches straight at the cuff, and I want to subtract another inch at the armhole, so that leaves 16 inches for shaping. Multiplying by 8 rows/ inch, that’s 128 shaping rows.
Next, I plug my numbers into the formula: 128 divided by 22 equals 5.8; rounding up to the nearest even number, I would work my shaping every 6th row.
But wait, you say. Won’t that be 132 rows, more than you’ve allotted for your shaping? Here’s how you’ll work the shaping: you’ll work 2 inches of cuff, then work your first shaping row. After that, you’ll work 21 more increases every 6th row, for a total of 21 x 6, or 127 rows. You then have one extra row to work above the shaping and before the armhole.
Note that in this example we ended up the lower number of shaping rows written in the pattern, so you could have used my quick and dirty method above.
Example 2: Shortening the Sleeve
Now let’s say you’ve gotten row gauge for the pattern, at 34.5 rows/ 4 inches, but you need to shorten the sleeve to 17 inches. Subtracting 2 inches for the cuff, and 1 inch above the shaping at the armhole, leaves you 14 inches. Multiplying by the row gauge gives you 120.75 rows, which we’ll round to an even 120 rows.
Dividing 120 by 22 gives you 5.5 rows between increases, so this time working the shaping every 6 rows won’t work. You could increase every 5th row and split the leftover rows between the cuff and the top of the sleeve. But we like to increase on right-side rows, so instead we’re going to work some increases after 4 rows and some after 6 rows.
It’s probably obvious to you without doing the math that working the increases every 4 rows will give us a lot of leftover rows, which will make our sleeve oddly shaped. So we’ll most of the increases every 6th row, and the remaining few every 4th row.
How? Well, if you divide 120 rows by 6, you will find you can work 20 increases every 6th row. Start with 18 increases every 6th row – that will take up 17 x 6 + 1 = 109 rows, which leaves 11 rows for the last 4 increases. But those will take 16 rows, so we’ll end up with more than 120 rows.
Instead, let’s try 16 increases every 6th row, and 6 increases every 4th. That will take 1 + 16 x 6 + 6 x 4 = 121 rows. Although that is one more row than you’ve given yourself for shaping, it will work just fine – we’ll make the cuff just a row or two shorter to compensate.
Other Uses of the Shaping Formula
To adjust the a-line waist shaping in the Composure Cardigan, or to add waist shaping to another garment pattern, you would use the same process. You can also use this formula to work one type of bust darts, which will be the subject of my next post.
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