Determining Good Fit
When you first purchase your bra you should fit it with the hooks fastened on the first hook which is the widest fitting. This way you can tighten the hooks as the bra stretches over time extending the lift of your bra. The underband around your body should be firm but comfortable. To test the firmness you should be able to run a finger comfortably under the band. If it is too tight, you can either let it out to a wider hook placement or you will need to swap the bra to one with a larger back size.
The back and front of the bra should be parallel to the waistline or slightly lower in the back. The lower edge of the band should anchor between the shoulder blades. The lower the back fits, the better the support.
The centre gusset should lie flat against the breast bone, not bridge away from the body. If it doesn't, your cup size could be too small, or the panel could be too small to accommodate the separation between your breasts.
Your underwires should lie flat against the sides of your rib cage, enclosing your breasts without rubbing or digging into the soft tissue of your armpit. If the underwire digs in or the breast bulges out the side of the bra, consider a larger cup size.
The cup should have a smooth outline, without your breast bulging out at the top or the sides of the bra. The cups also should not pucker or wrinkle anywhere.
The bra should support the weight of your breasts mainly with the underband. The cup and shoulder straps will share the remaining amount of support.
Check your silhouette. The bust should be midway between the top of the shoulder and the bend of the elbow, to create a silhouette of balanced proportions.
Problem: The breast is spilling out the top of the cup, and the cup is cutting in.
Solution: The cup size is too small. Increase the cup size until the breast fits smoothly into the cup.
Problem: The cup is wrinkled and is over-covering breast and the breast does not fit securely inside cup.
Solution: The cup size is too big. Decrease the cup size until the breast fits smoothly into the cup and there is no wrinkled fabric.
Problem: The cup does not sit against the top of the breast and is gaping.
Solution: The cup size is too big. Decrease the cup size until the breast fits smoothly and there is no gaping at the neckline.
Problem: The underband rides up at the back or is sitting too high.
Solution: The bra body is too big or the strap has not been adjusted and is too short in length. Try a body size smaller, or lengthen the strap until the underband is positioned correctly.
Problem: The shoulder straps are digging into the shoulder.
Solution: The strap has not been adjusted to suit your body shape and is too short in length. Adjust the back strap (loosen with the slide) until the strap fits comfortably on the shoulder.
Problem: The shoulder straps are falling off the shoulder.
Solution: Either the strap has not been adjusted to suit your body shape and is too long in length in which case you can adjust the back strap until the strap fits comfortably on the shoulder. It also could mean that the back of your bras is too big causing the straps to sit on out on the edge of your shoulders. Check the back size and potentially go down a back size.