One more very important thing to take into consideration when designing / knitting a sweater: how much ease will you be building into the design? The great news is, you’re the boss of this pattern, so if you want it to fit tightly (negative ease,) just skimming the skin (neutral ease,) or loosely (positive ease,) you can build this style consideration into your design with a bit of guidance.
One simple approach to this is to choose a sweater from your personal collection of favorite sweaters, purchased or homemade, which you love the fit of, and pattern the ease of your design after that sweater. This works especially well if the weight of the example sweater’s fabric is similar to what you are designing. By laying the example sweater out on a flat surface, unstretched, and taking careful measurements at all of the important locations (neckline, shoulder length, chest, waist, armskye, arm length, hip, cuff, back length) you will have your patterns proportions all set. From there you apply your gauge to each of those measurements (rows per inch x inches of vertical measurements, and stitches per inch x inches of horizontal measurements,) and you will have the basic outlines of your pattern. Increases and decreases will then need to be distributed between measurement points.
Another approach is to work from your “gauge x measurement” numbers and then add a certain amount of inches for the various amounts of ease you desire. This is a bit more complicated, but is described nicely over at oliveknits.com. Here are her definitions of the various levels of ease:
Negative ease: A garment which measures smaller than the measurements of the body (usually in the bust, with the corresponding fit in the arms and body being proportional to the fit at the bust). For example, if you have a 36″ bust and you knit a sweater with negative ease, the resulting piece will measure less than 36″. How much less will depend on how much negative ease is written into the pattern.
Zero ease: A garment which measures the same as the measurements of the body. For example, if you have a 44″ bust and you knit a sweater with zero ease, the resulting piece will measure 44″ at the bust.
Positive ease: A garment which measures larger than the measurements of the body. For example, if you have a 32″ bust and you knit a sweater with 3″ positive ease, the resulting piece will measure 35″ at the bust.
She goes into detail about how to tell what the ease is in a pattern, but since you are creating your own design, all you need to do is add the desired ease amount to the bust and waist measurements in your design (and a smaller more appropriate amount to your sleeves widths.)
