While wearing a bra, wrap a tape measure snugly, but not too tightly, around your rib cage just under the lower edge of your bra. Add 5 inches to that measurement to determine your band size. If this measurement is an odd number, round it up by one inch. To determine your cup size, measure over the fullest part of your bust. The difference between this measurement and the band measurement will give your proper cup size. If the difference is:

Size Conversion — BRASSIERES

U.S.A.	EURO	FRANCE	U.K.	ITALY	SPAIN
30	65	80	30	1	80
32	70	85	32	2	80
34	75	90	34	3	90
36	80	95	36	4	95
38	85	100	38	5	100
40	90	105	40	6	105
40	90	105	40	6	105
42	95	110	42	7	110
44	100	115	44	8	115
48	105	120	46	N/A	120
N/A	110	125	48	N/A	125

How to know if straps are adjusted correctly?

U.S.A.	EURO	FRANCE	U.K.	ITALY	SPAIN
XS	36	38	XS(1)	2	38(1)
s	38	40	s(2)	3	40(2)
M	40	42	M(3)	4	42(3)
L	-	-	-	-	-
XL	44	46	XL(5)	6	46(5)
XXL	46	48	XXL(6)	7	48(6)
XXXL	46	48	XXL(6)	8	50(7)

As a bra gets larger in the band size, the distance between the cups also increases. Underwires are placed in a bra according to accurate measurements. If you experience poking, your bra is probably the wrong band size. It is important that you measure for your band size and then not deviate from it when purchasing bras.

When the frame of your bra is not giving you adequate support, the shoulder straps are forced into providing additional support. The most common reason for digging shoulder straps is the band size being too large. Full-figured women know the bra sizing game all too well. For example, if she is a 38E and the bra she wants only goes as high as a “D” cup, she will go up a band size and down a cup size and think it fits (40D). However, she has done a disservice to herself because going up a band size means her straps are going to have to make up for the support lost in the increased band size. To relieve shoulder strap pain, measure yourself and stick with the correct bra size.

Centre your nipples above the apex point of your bra. Then, you’ll have a plumper top to your breast volume.

Can you slip a finger under your straps? If you can’t, or if the straps are digging into your shoulders, you’ve probably over-adjusted to compensate for a bra that’s the wrong size. Usually, the band size is too large. Straps should have just enough tension to hold the bra on your shoulders; they should provide about 10% of a bra’s support. So, do the strap test - Slip your straps off your shoulders so they are resting on your arms. A well-fitting bra should stay on (with some sagging) without the straps’ assistance.