All my patterns follow the CYC sizing standards.
Source: Craft Yarn Council
The sizes are indicated in two different ways.
1) Sizes and finished measurements are indicated
2) Only finished measurements are indicated
When only finished measurements are indicated, it is either because I wanted to have more sizes than these letters (S, M, L…) would have allowed me or the pattern of the garment didn’t make it possible to have all these sizes.
When only finished measurements are indicated, you may want to consider the following things:
Some people like their garments with negative or positive ease and others don’t. In the case of negative ease, the bust measurement of the garment is smaller than your actual bust size and the garment has to stretch a bit to fit you. Positive ease means that the bust measurement of the garment is larger than your bust measurement and there is some space between the garment and you. There is also zero ease, in which case the two measurements are the same.
I always indicate the size and ease of the sample shown in the pictures.
It is wise to compare the measurements of the chosen garment to your favourite ones before you start knitting to avoid nasty surprises. (And please swatch to make sure that you really are knitting the size you want to.)