A bra that fits correctly will be comfortable. You wonâ€t be able to feel the hook and eye, nothing will dig in or scratch, and the straps wonâ€t slip off.
The bra's cups will fit the shape of your breast â€” no gap and no spilling over the top or to the side.
The straps will sit snuggly on your shoulders without digging in or falling off. Of course, you can adjust the straps to fit better, but if adjusting doesnâ€t help, then the band size is likely wrong