Bra Cup Size Chart: How to Read It

To read a bra cup size chart, find your band size first, then work out the gap between your bust measurement and your band measurement. Each step up in that gap is one cup letter, so a larger gap means a larger cup.

This guide is for shoppers and for store owners who want to explain the chart clearly. It sits alongside our overview of AI size recommendation for fashion stores, which shows how stores can match body measurements to their own charts.

What are the two parts of a bra size?

A bra size has a number and a letter, such as 34B.

• The number is the band size. It describes the ribcage, just under the bust.
• The letter is the cup size. It describes how much fuller the bust is than the band.

The letter is not a fixed volume. A D cup on a small band holds less than a D cup on a large band. This is why two people with the same cup letter can need very different bras.

How do you find your band size?

Measure snugly around your ribcage, directly under the bust, with a soft tape. Keep the tape level and breathe out normally.

Take the measurement twice and use the average, because the tape can slip. Wear a thin, unpadded bra or none, so the reading is not inflated.

Brands round that number to the nearest band size on their chart. Some brands add inches to the underbust to get the band size, while others use the measurement directly. This is a common reason sizes differ, so read the instructions printed next to the chart. Many charts list the band in inches for US and UK sizing and in centimeters for EU sizing. Check which one your brand uses.

How do you work out the cup size?

Measure around the fullest part of the bust, then subtract the band measurement. The difference gives the cup.

Here is a worked example. The numbers are made up to show the method.

1. Band measurement under the bust: 32 inches, so the band size is 32.
2. Bust measurement at the fullest point: 35 inches.
3. Difference: 3 inches.
4. Look up 3 inches on your brand's chart. On many US charts that is a C cup, giving 32C.

Difference (bust minus band)	Typical US cup letter
1 inch	A
2 inches	B
3 inches	C
4 inches	D

This is an example chart that shows the pattern, so check your brand's own chart. Letters above D differ more between brands and regions. For those, use the brand's table, and see our bra size conversion between UK, US, EU and AU guide.

What are sister sizes?

Sister sizes are bras with the same cup volume but a different band and letter. If you go up a band size, you go down a cup letter to keep the cup volume similar.

For example, 34B and 32C are sister sizes. This helps when a band feels too loose or tight but the cups fit well.

How can you tell if the chart gave you the right size?

A chart is a starting point. Use these checks when you try the bra on:

• The band sits level around your back and does not ride up.
• The center panel (the gore) lies flat against your breastbone.
• Your breast tissue fills the cup without spilling over or leaving gaps.
• The straps stay in place without doing most of the supporting.

Try the bra on the loosest hook first. Bands stretch over time, so you will move to tighter hooks as the bra ages.

If it fails more than one check, move to a sister size. Our guide on how a bra should fit covers each check in more detail.

How should stores present a cup size chart?

Shoppers read a chart quickly and often on a phone. A cluttered chart leads to wrong guesses.

If you sell bras, show the chart in the unit your customers use and say which region it follows. Add a one-line how-to-measure note next to the chart.

Fit varies by style, so say whether a style runs small or has a stretchy band. Reducing fit-related returns starts with clear information, as described in where fit-related returns come from.

Other garments have their own reading rules too. See how to read a men's suit size chart or a unisex hoodie size chart.

FAQs

Is a bigger cup letter always a bigger bust?

No. Cup letters are relative to the band. A 38D holds more volume than a 32D, even though both are D cups.

Why does my cup size change between brands?

Brands use different sizing systems, patterns and stretch. Check each brand's own chart rather than assuming your usual size.

What if I fall between two cup sizes?

Try the smaller cup in a style with stretch, or the larger cup in a non-stretch style. Then check the fit points above.

Do I need to remeasure over time?

Yes, now and then. Weight changes, pregnancy and other life changes can shift both band and cup.