Choosing the right size to make is one of the most important things you can do.
If you have a large bust and chose a size using that measurement then it is unlikely you will get a good fit in the neckline and shoulders, and that area will end up being oversized. If you have a larger bust, you should always choose the size based on your high bust measurement. You can then add any alterations needed to make your full bust fit as well, such as an FBA for sewing or short rows for knitting.
Full Bust: What you would normally think of as just ‘bust’. It is the measurement around the largest part of your chest.
High Bust: This is the measurement around your body, directly under your underarms.
If you do not have a large bust and clothes normally fit you without having to size up for your chest then you can just use your normal bust (full bust) measurement when choosing a size.
If you have a large bust you might find you typically have to size up in clothing to get it to fit over your chest. When you make your own clothing, the better way to do this is to make the size the rest of your body needs (i.e. the size based off your High Bust) and then do an adjustment for your Full Bust. This means your shoulders and neckline will fit perfectly because they haven’t been made larger to account for a bigger bust. In this case, you would do a FBA (Full Bust Adjustment) which is usually straightforward and will not change your neckline or sleeve size.
Now that you’ve chosen the proper size to make sure the neckline, shoulders and bust sized properly you are on the right track to a successful fit!