I've talked to you in the past about how to increase and decrease, but how do you know when to increase or decrease? Often a pattern will tell you very explicitly how to place your increases or decreases, for example:
Next Row (Increase Row - RS): K1 (4, 1, 4, 1), kfb, k4, p1, k5, p1, k4, kfb, (k5, p1) 1 (1, 2, 2, 3) times, k3, kfb; (p1, k1) 3 times - 37 (40, 43, 46, 49) sts.
As you can see, this pattern is telling you to work a certain number of stitches for the size you're making, then make an increase, then work some more stitches, and so on across the row. However, sometimes what you will see instead is "Increase 3 stitches evenly spaced." How do you figure out where to put (or take away, if you're decreasing) the stitches then? Well, you do a little quick math.
Let's think for a minute about why you want to space out these stitches: if you don't, you end up with a big clump of extra fabric in one spot and a tight spot in another. What you want is a nicely balanced piece of fabric that shrinks or expands evenly, not a lopsided lump. To make this happen, you want to place these shaping stitches about the same number of stitches apart. To determine the number of stitches between your shaping stitches, divide the current number of stitches by the number to be increased or decreased.
Here are a couple of examples:
- You have 60 stitches and you are told to increase 6 stitches evenly across. 60 ÷ 6 = increase at every 10th stitch. This one's easy, because it works out evenly, but what if...
- You have 99 stitches and you are told to increase 8 stitches evenly across. 99 ÷ 8 = 12.375. You obviously can't increase every 12.375 stitches, so you need to increase mostly at every 12th stitch and add a couple of 13s in there. The math and distribution frequency starts to get a little complicated at this point, but when you see unbalanced stitch counts like this it's usually something that's not going to be very visible (like at the transition from ribbing to stockinette). This means you can fudge it a little and not be too terrifically concerned if you end up with a couple of extra stitches at the end of the row or have two 13st sets in a row. Focus on getting the right number of increases and relatively even spacing.
- You have 80 stitches and you are told to decrease 10 stitches evenly across. Now we're back to easy, right? 80 ÷ 10 = every 8th stitch decreased. Ah, but decreases are a little trickier...you actually have to think about which stitches you are using for the decrease...you are decreasing the 8th stitch, so your next stitch in the count is going to be "1". If you use that stitch in your decrease, your count becomes unnecessarily complicated, so instead, use the stitch before the decrease stitch. This means that you would, in this case, work six and then use stitches 7 and 8 to work the decrease.
One final tip: You may find that when you are working on flat pieces you prefer to offset your beginning and ending stitches to preserve a selvage. This is a really great idea -- just make your first increase or decrease in the middle of the first set of stitches, and then the final shaping will occur in the middle of what would have been the final set of stitches. To go back to our first example, you would work your first increase at stitch 3 (because half of 6 is 3) and your final increase would be worked three stitches from the end of the row.
When in doubt, remember to think about the big picture: your end goal is a balanced piece of fabric. Don't be afraid to do a little math to get there!