Before You Begin: BasicsOccasionally a pattern may call for a yarn that has been discontinued. This happens often in the knitting world, as yarns can be seasonal or can stop being made for various reasons. Or maybe you like a pattern but want to use a different yarn. Either way, if you are going to use a different yarn, it is important to check the gauge to make sure you are going to get the correct amount of stitches per inch. Otherwise the garment won't have the proper fit. To check the gauge, just knit a swatch and remove it from the needle, stretching it out a little. If your gauge is below the size in inches it should be, change to a bigger needle for a looser stitch and try again. If it's too small, change to smaller needles for a tighter stitch and try again.
Patterns usually list the different sizes you can knit an item in. For this pattern, you can determine your size by loosely measuring the fullest part of you chest with flexible measuring tape and then referring to this grid:
Petite: 29"-31" (finished size: 30")
Small: 32"-34" (finished size: 33")
Medium: 35"-37" (finished size: 35")
Large: 38"-40" (finished size: 39")
Gauge
13 stitches = 4"