How I design a top-down raglan pullover
This one special thing is the depth of the back neck. This is determined by how many stitches are cast on for the sleeves at the neck edge. Half of the sleeve cast-on measurement determines the back neck depth (and the front neck depth if it is worked the same as the back). This measurement, when added to the length of the raglan shaping determines the total length from the shoulder to the underarm, and is important to include for the desired armhole length to be accurate.
For example, if you have 4″ worth of stitches cast-on at the top of the sleeve, that would result in a 2″ back neck depth. And, if the raglan shaping is worked over 5.5″, the total armhole depth is 7.5″. This is an important thing to keep in mind when writing the raglan shaping, because a 5.5″ armhole is a lot smaller than a 7.5″ armhole (Read More at…. http://kristentendyke.blogspot.com/2013/06/how-i-design-top-down-raglan-pullover.html)