If you've ever wondered what the difference is between a B cup and a C cup, or why your bra size seems to change between brands, you're definitely not alone.

Bra sizing can feel confusing, especially when you're faced with a seemingly endless combination of numbers and letters. But understanding how cup sizes work can make finding your perfect fit much easier.

Let's break it down.

Bra Size Is About Two Measurements

Your bra size is made up of two parts:

Band Size
This is the number part of your bra size and refers to the measurement around your ribcage, just underneath your bust.

Cup Size
This is the letter part of your bra size and refers to the volume of your breasts in relation to your band size.

The important thing to remember is that cup size doesn't exist on its own. A D cup on a 32 band is very different from a D cup on a 40 band.

How Are Cup Sizes Calculated?

Cup size is worked out by comparing your bust measurement to your band measurement.

The bigger the difference between these two measurements, the larger the cup size.

As a general guide:

A Cup = 1 inch difference

B Cup = 2 inch difference

C Cup = 3 inch difference

D Cup = 4 inch difference

DD/E Cup = 5 inch difference

F Cup = 6 inch difference

G Cup = 7 inch difference

And so on.

Each cup size typically represents around one inch of additional breast volume.

Why Cup Letters Can Be Misleading

One of the biggest bra myths is that a D cup is automatically a "big" size.

In reality, cup size is relative to the band size.

For example:

A 30D has significantly less breast volume than a 38D.

That's why focusing on the full bra size rather than just the cup letter is so important.

At Tutti Rouge, we hear women say "I'm only a D cup" all the time. The truth is, the letter alone doesn't tell the whole story.

What Are Sister Sizes?

Sister sizing is one of the most useful bra fitting tricks you can learn.

Sister sizes have the same cup volume but a different band size.

For example:

34C

32D

36B

These sizes all hold a similar breast volume, but the fit around your ribcage will feel different.

If your cups fit perfectly but your band feels too tight or too loose, sister sizing can help you find a more comfortable fit.

Why Bra Sizes Vary Between Brands

Ever tried the same size in two different brands and found they fit completely differently?

You're not imagining it.

Different brands use different fit models, materials, and construction methods, which can all affect sizing.

That's why it's always worth trying different styles and keeping an open mind about the size on the label.

The perfect fit is far more important than the number or letter.

Breast Shape Matters Too

Cup size is only part of the story.

Breast shape, fullness, and how breast tissue is distributed can all affect how a bra fits.

This is why two women wearing exactly the same bra size may prefer completely different bra styles.

Some women love balconette bras for lift and shape, while others prefer a plunge or full coverage style.

The best bra is always the one that feels comfortable and makes you feel confident.

Finding Your Perfect Fit

Understanding bra cup sizes is a great starting point, but the most important thing is finding a bra that works for your unique shape and body.

A well-fitting bra should:

Sit snugly around your ribcage

Fully contain your breast tissue

Feel supportive without digging in

Stay comfortable throughout the day

When in doubt, a professional bra fitting can make all the difference.

Because confidence starts with a bra that fits properly.

The Bottom Line

Bra cup sizes are simply a way of measuring breast volume in relation to your band size. Every cup size represents a small increase in volume, but the fit will vary depending on your body shape, band size, and the style of bra you choose.

The number and letter on the label are just a guide. What really matters is how your bra feels.

And when it fits properly? You'll know.