Bra Tape Measure across rib cage under bra

1. Measure Your Band

Wearing an unlined bra, take a measuring tape across your back and wrap it snugly around under your bust. Make sure the tape is level across your body.

If your measurement is an odd number, round up +1 inch, if it's an even number, that's your band size. For example, a 29" measurement would be a 30" band size; a 30" measurement would be a 30" band size.

Bra Tape Measure across apex of boobs

2. Measure Your Bust

Standing straight, take the measuring tape around your back to the fullest part of your chest across the apex. The tape should feel comfortable around your chest, not too loose, not too tight. Round to the nearest whole number.

Bra band and cup measurement size chart calculation

3. Calculate Your Bra Size

Take your Bust Measurement (step 2) minus your Band Measurement (step 1) . Generally, 1" represents a cup size (refer to the chart on the left).

For example, if your bust measurement is 34" minus your band measurement of 29" = 5". This 5" difference is a DD cup. Add your cup size to your band size (determined in step 1) = your bra size, 30DD. 

Bra Cup and Band Sister Size Chart Rainbow Chart

4. Sister Sizing

If your bra doesn't feel comfortable, try "sister sizing." For every band size you go up, you should go down one cup size.

For example, if you are a size 30DD, your sister sizes are 28F and 32D. If your bra feels too tight, try sizing up to 32D. If your bra strap is riding up your back, this is a sign that your bra is too big, try sizing down to a 28F.

  • Bra band too big and loose on body, riding up back.


    ❌ Rides Up – A band that rides up is a sign the band is too big.
    ❌ Back Bulge – If your skin is bulging over your band, your band is too small.

  • Bra on body back view, 3 hooks


    ✔️ Smooth & Flat – Your band should lay flat and straight against your back.
    *This is extremely important for large chested women as the support and lift comes from the band (not from the strap).

  • Bra brand hook start at the loosest hook


    ✔️ Loosest Hook – A newbra should be worn comfortably on the loosest hook. The band will stretch over time which is when you can move to an inner hook to tighten. 
    ❌ Tightest Hook – If you have to wear it on the tightest hook right away, your band is too large.

  • Incorrect bra size, bra strap falling down off shoulder


    ✔️ Straps should lay snug against your shoulders and stay in place throughout the day. 
    ❌ Slips Off – If your straps continue to slide down even after you tighten them, it may be time for a new bra. 
    ❌ Digs In – Straps that dig in and leave marks on your shoulders indicate that your band size is too large. The straps are doing more support work than they are supposed to. Try a smaller band. 

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  • Properly fitting bra, right bra cup and band size


    ✔️ Cups should lay flush against your breast, providing lift and shape.

  • Bra cup too big, gaping on chest on top of boob


    ❌ Gape – Cups that gape when you bend over or lie down indicates that your cup size is too large.
    ❌ Wrinkle – Cups that wrinkle is also a sign that the cup is too big or may not be the right shape cup for your breasts. Try a smaller cup or a different style bra such as a demi cup.

  • Bra cup too small showing cleavage overflowing


    ❌ Overflow – Cups that cut into your skin with spillage on top or sides mean the cup is too small. Go up a cup size.

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