If you just want a triangle, there's a very easy pattern that you stop when you think it's the right size.
Cast on 3 stitches. Then k1, yo, knit across. Do this on every row, and it will grow bigger and bigger. Stop when it's as wide at the top as you'd like it to be. You can do it with any size yarn and needles, too.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry