When Triangles Go Right

Some triangles are harder to knit than others. Here is how to tame them.

All triangles can be divided into two right triangles. If you put the longest side on the bottom, and drop a line straight down from the peak, you have divided the original triangle into two right triangles.

 
(If two sides of the original are equal to each other, pick either one. If all three sides are equal, pick any of them.)

Not being a sweater knitter, this is the one time I pay attention to gauge. If you are using garter stitch, then your gauge (horizontal) is equal to your row gauge (vertical); specifically, one stitch is equal to one ridge (two rows). You can think of each part as a small square, and can graph out shapes easily on regular graph paper.

If you are using stockinette stitch, it's trickier. I generally measure, but it is roughly a 4:3 ratio (4 stitches = 3 rows, because each stitch is taller than it is wide). This is why there is special knitter's graph paper which you can use to chart out stockinette patterns. If you are using some other stitch, then you have to measure to get your gauge and row gauge.

Using your gauge, figure out how many stitches you need for line A, and then using your row gauge, figure out how many rows you need for line C. Now you know how long you have in which to decrease down to zero from line A. For a super simple example, if A = 20 stitches and C = 10 rows, you have to decrease 20 stitches in 10 rows, so you have to decrease 2 stitches in each row.

Now do the other side. If B = 5 stitches, then you have to decrease 5 stitches in 10 rows, or 1 stitch every other row.

Now you can knit the entire triangle. Cast on A+B stitches (20 + 5 in the example), and then on the right edge, decrease one stitch every other row, and on the left edge, decrease 2 stitches each row, as you go back and forth. That will give you a triangle of the shape you wanted.