Ideally, you should be aware of your exact bra size so that you can purchase bras that feel and look perfect at the moment you are buying them. However, as a woman, you know that bras do not always wind up fitting as well as you would like. Sometimes, you see a bra that is the right cup size but the wrong band size on sale for an irresistibly low price. Other times, you buy the size that normally fits you perfectly only to find that, for some reason, that particular brand's sizes run a little bigger than usual. Whatever your reason for winding up with a bra band that is too big to fit your chest, you can alter the band at home until the bra is a perfect fit.
Try loosening both straps and hooking your bra band on a tighter notch before you begin to alter the bra. Sometimes, women try to lift their breasts by tightening their bra straps more than is necessary. However, because all breast support is supposed to stem from the band rather than the straps, the only thing accomplished by tightening the straps too much is making the bra band ride up the wearer's back and appear too big. If your bra band still seems too big after you try this step, move on to Step 2.
Put on the bra with the band unhooked. Pinch both ends of the band to fit in the back. Then, have someone draw lines on each band 1 inch from the points where you have pinched. The 1-inch leeway is there so you will have room to sew the clasps back on in later steps. If there is no one available to help you, it is possible to mark the band on your own, but it will require some skillful maneuvering on your part to pinch and mark the bra at the same time. Another option is to put the bra on backward so you can mark the band in the front, but this may result in a less precise measurement and only works for small-breasted women.
Use a pair of scissors or another pointed object to remove the stitching holding the bra clasps onto the band. Set the clasps aside.
Cut the band along the lines that you drew earlier. Throw away the excess material.
Insert the new ends of the band back into the clasps, and sew them into place. If you are using a sewing machine, set it to a zigzag stitch to match the original stitching that manufacturers use to sew on most bra clasps.