I always go to the “click here” measurements that are in the description for the item. There you can look at every size and see what the bust measurement is, which is the measurement that is 1 inch lower than armpit.
Then based on the fabric you can decide, some fabrics are so stretchy you can go with something that’s very close to your actual measurement, but if it isn’t stretchy you will have to factor in an inch or two just for comfort.
Once you get used to looking at this measurement you can’t go wrong, and you will also discover that there are is a very wide range based on the vendor even in the same size.
Logo is notorious for having a wide range for a size medium based on the item.