How to Measure Your Bra Size: The Rib Cage Method

Your bra size is your rib cage measurement rounded to the nearest even number for your band size, plus the difference between that number and your bust measurement to find your cup size. This is BRABAR's EZ-fit rib cage method — the most accurate way to find your bra size at home, without a fitting-room visit or a formula that adds inches on top of your real measurement.

Step 1: Measure Your Band Size

Wrap a soft measuring tape directly around your rib cage, just underneath your bust. Keep the tape level and snug, not tight. Round the result to the nearest even whole number — that's your band size.

• 28.5 inches rounds down to a 28 band.
• 29 inches (exactly between 28 and 30) rounds up to a 30 band.
• 32 inches stays a 32 band.

Step 2: Measure Your Bust Size

Wrap the tape around the fullest part of your bust, keeping it parallel to the floor. Round to the nearest whole number.

Step 3: Subtract Band From Bust to Get Cup Size

Subtract your band measurement from your bust measurement. Each inch of difference equals one cup size, starting at A:

• 1 inch = A cup
• 2 inches = B cup
• 3 inches = C cup
• 4 inches = D cup
• 5 inches = DD/E cup
• 6 inches = DDD/F cup

Worked Example

Rib cage measurement: 32 inches → band size 32. Bust measurement: 36 inches. 36 − 32 = 4 inches → D cup. Bra size: 32D.

Why the Rib Cage Method, and Not Plus-4 or the Armpit Method?

Two other methods are common in the US, and both distort the result:

• The plus-4 method adds four inches to your underbust measurement before calling it your band size — still used by calculators from brands like SKIMS and Aerie. It produces a band that's too loose to actually support anything.
• The armpit method, the one Victoria's Secret's own instructions describe, measures higher up on the torso near where the straps meet the cup. Because the body is wider there than at the rib cage, this also inflates the band number.

The rib cage method skips both shortcuts. It measures the band where it actually sits and uses the real number — no rounding conventions borrowed from an era of stiffer, less-adjustable fabric.

Frequently Asked Questions

What is the rib cage method for bra sizing?

It's a two-measurement method: your rib cage measurement (rounded to the nearest even number) gives you your band size, and the difference between your bust measurement and that band size gives you your cup size in inches, converted to a letter.

Do I need to add inches to my band measurement?

No. Round your direct rib cage measurement to the nearest even number and use that as your band size. Adding four inches on top (the plus-4 method) produces an inaccurate, oversized band.

Why does Victoria's Secret give me a different size than BRABAR?

Victoria's Secret's measuring instructions use the armpit method, measuring higher on the torso than the rib cage. Because that part of the body is wider, it produces a larger band number for the same person.

What if my measurement is an odd number?

Round up to the next even number. A 29-inch rib cage rounds up to a 30 band.

Does cup size mean the same thing on every band size?

No. Cup size is relative to band size — a 28D and a 36D hold different amounts of breast tissue. The letter only tells you the difference between band and bust, not an absolute volume.

Ready to shop your size? Explore BRABAR's full range of bras by band and cup size, or use our Fit Guide and Bra Size Calculator to walk through these steps with your own measurements.