How to measure your bra size at home

Most women are wearing the wrong bra size, and it is almost never their fault. Sizing is inconsistent between brands, rarely explained, and the advice you get in a shop often contradicts the advice you got in the last one.

Here is the method that actually works, and the reasoning behind it.

The short version: measure snugly around your ribcage, just under your bust, and round to the nearest even number — that is your band. Then measure loosely around the fullest part of your bust. Each inch of difference between the two is one cup size: 1 inch is an A, 2 is a B, 3 is a C, 4 is a D.

What you need

A soft measuring tape, a mirror, and an unpadded bra — or none at all. A padded bra adds volume that will throw the bust measurement off.

Step one: measure your underbust

Run the tape around your ribcage, directly under your bust. Keep it level all the way round — check the back in a mirror, because a tape that rides up behind you will read small.

Pull it snug. This measurement should feel firm, not loose, because the band is meant to be firm. Breathe out normally and read the number.

Round to the nearest even number. That is your band size. If you measure 31 inches, your band is 32. If you measure 33.5, your band is 34.

Step two: measure your bust

Run the tape around the fullest part of your bust, keeping it level and flat. Do not pull it tight — the tape should rest against you without compressing anything.

Step three: find your cup

Subtract your band size from your bust measurement. Each inch of difference is one cup size.

So a 32 inch band with a 36 inch bust is a 4 inch difference — a 32D.

If you would rather not do the arithmetic, our size calculator does it for you, and gives you sister sizes to try as well.

The part nobody tells you: the band does the work

Around 80% of a bra's support comes from the band, not the straps. This single fact explains most bad bra experiences.

If your band rides up your back, it is too loose — and your straps are compensating, which is why they dig in. The instinct is to tighten the straps. That makes it worse. The fix is a smaller band.

Your band should sit level all the way round, and you should be able to slide two fingers underneath, no more.

A band sitting level, front and back — our Full Coverage Non-Padded Cotton Bra. An unpadded style like this also gives the truest bust measurement.

Sister sizes, and when to use them

Cup volume is relative to band size. A 34C and a 32D hold roughly the same volume — they are sister sizes.

This matters when your size is sold out, or when a style runs slightly small. Going down a band means going up a cup, and vice versa:

• 34C runs tight in the band? Try 36B.
• 34C gapes at the cup? Try 32D.

Signs the fit is wrong

• Band rides up at the back — band too loose, go down a size
• Straps dig into your shoulders — the band is not doing its job
• Cup gapes or wrinkles — cup too big, go down a cup
• Spillage at the top or sides — cup too small, go up a cup
• Underwire sits on breast tissue — cup too small, not band too tight

{{product:u-shape-back-seamless-padded-bra-women | Moulded stretch cups that follow your shape}}

Measure again every so often

Body shape changes with weight, age, pregnancy and time. Bands also stretch: even a well-made bra loosens over six to twelve months of regular wear, which is why you start on the loosest hook and work inward.

Re-measure once a year, and whenever a bra that used to fit suddenly does not.

Shop this guide

• Full Coverage Non-Padded Cotton Bra — unpadded and soft — also the best bra to measure in
• Seamless Full Coverage Light Padded Bra — light padding, smooth under fitted tops
• U-Shape Back Seamless Padded Bra — seamless moulded cups, invisible under clothes
• Racer Back Padded Bra — straps that cannot slip, sizes S to XXL

Frequently asked questions

Why does my bra size come out different on different calculators?

Some calculators still use the older method of adding 4 or 5 inches to your underbust. That gives a band two sizes bigger and a cup smaller than the modern method used here, where the band is simply your underbust rounded to the nearest even inch. If bras in your old size ride up at the back, this is usually why.

Should I measure my bra size with a bra on or off?

Off, or in an unpadded, wire-free bra. Padding adds to your bust measurement and makes the cup come out too big.

What if my measurements fall between two sizes?

Round your underbust to the nearest even number. If that band then feels tight, try the sister size: one band up and one cup down — for example 34B instead of 32C.

How do I find my size in So Glamy bras?

Our bras are sized S to XXL rather than by band and cup, and each size covers two band sizes: S fits a 30–32 band, M fits 32–34, L fits 34–36, XL fits 36–38 and XXL fits 38–40. Every bra page shows the full chart under "Size chart". If you are between two sizes, choose the larger one — or message us on WhatsApp with your measurements and we will tell you which to order.

How often should I measure my bra size?

Once a year, and again after any weight change, pregnancy or breastfeeding, or whenever a bra that used to fit stops fitting.

Does bra size change during periods?

Many women find their bust a little fuller and more tender in the days before a period. A soft, stretchy, wire-free bra is usually more comfortable then than a firmly shaped one.