Sizing your maternity bra is important. It's something you'll wear often and it has to fit properly to be comfortable.
Note: You should buy your maternity bra at the beginning of your second trimester.
Wearing a non-padded bra, wrap the tape around your bust over your bra at the fullest point. Keep the tape level around the back and fairly loose around the body.
Wrap the measuring tape tightly under your bust around your rib cage. Be careful to keep the tape level from front to back. Exhale fully, pull the tape tightly around your body, then round your measurement up to the nearest inch/cm.
Example: 32" bust + 4" = 36 band size
After measuring, subtract your band size from your bust size. Find that number on the chart below to get your cup size.
Example: 40" - 36" (Band) = 4" (D)
Your Bra Size is your band size plus your cup size. Example: 36D