What's the real difference between an A cup and a B cup? Or a D and a DD? This cup size comparison shows what each size actually means — in inches, volume, and everyday terms. Whether you're comparing A cup vs B cup, B cup vs C cup, or C cup vs D cup, this guide covers every step.
This cup size comparison shows how each letter differs in real terms. Cup size isn't a fixed volume — it's the difference between your bust and underbust measurements. An "A cup" simply means a 1-inch difference. A "D cup" means a 4-inch difference. The letter tells you the gap, not the absolute size.
This is why a 32D and a 38D look nothing alike. The D refers to the same 4-inch difference, but on a 32 band vs a 38 band, the actual cup volume is quite different. If you want sizes that share the same cup volume across different bands, that's what sister sizes are for.
Want to know your actual size before comparing? Try our bra size calculator first.
Our visual cup size comparison below shows approximate volume at band 34. Hover for details.
Volumes are approximate and vary by band size. A D cup at band 32 is smaller than a D cup at band 38.
This cup size comparison continues with real visuals. These four women all wear the same band size — the only variable is cup volume.
From A cup (1-inch difference) to DD cup (5-inch difference). Each letter adds approximately one inch of bust projection.
Less than one inch of difference between bust and underbust. The smallest standard cup size. If you're looking for an AA cup size bra, specialty brands and bralettes are your best options. Common in teens and petite frames. Approximate volume at band 34: around 65 ml. Bralettes and unlined styles tend to fit best.
One inch of difference. A subtle curve that's well-suited to triangle bras and lighter support. Volume at band 34: roughly 130 ml. Many women sized as an A in stores actually measure as a B or C with proper fitting — the +4 method systematically undersizes cups.
Two inches of difference. A moderate cup that works across most bra styles. Volume at band 34: about 200 ml. Often considered "average" in the US, though actual average sizes trend larger. The jump from A to B is noticeable in fit but subtle visually.
Three inches of difference. Full enough to benefit from underwire support in most styles. Volume at band 34: approximately 275 ml. One of the most commonly stocked sizes, widely available across brands.
Four inches of difference. Despite its reputation, a D cup isn't necessarily "large" — on a 30 band, it's quite compact. Volume at band 34: around 360 ml. Good support and well-fitted straps start to matter here.
Five inches of difference. The most commonly purchased size in the US is 34DD. In UK sizing, DD is the same. After this point, US and UK cup letters diverge. Volume at band 34: approximately 450 ml.
Six inches of difference. This is where US and UK sizing splits — the US calls it DDD or F, the UK calls it E. Volume at band 34: about 550 ml. Full-coverage and minimizer styles become popular. Understanding the DDD cup size is key — it's the same as an F cup in US sizing.
Seven inches of difference. Specialty brands like Elomi, Panache, and Freya become the go-to options, as most mass-market retailers stop at DD or DDD. Volume at band 34: roughly 660 ml. Proper fit becomes crucial for comfort.
Eight or more inches of difference. Sizes continue through I, J, K, and beyond in both US and UK systems (though the letters don't match). Volume at band 34 for an H cup: around 780 ml. Specialty retailers and online shopping become essential.
Most people imagine a "D cup" as objectively large. In reality, as this cup size comparison demonstrates, a D is just a 4-inch difference — and on a 30 band, that looks very different than on a 40 band. Cup letters only describe the proportion between your bust and ribcage, not an absolute volume. This is exactly why using a calculator with your actual measurements matters more than guessing from a letter.
Need to find your measurements first? See our measuring guide for step-by-step instructions.
After reviewing this cup size comparison, check the complete size reference across all international systems in our bra size chart. To find sizes with the same cup volume on a different band, try our sister size finder.
