Lingerie Sizing Conversion: A Simple Guide to Band and Cup Letters

Quick answer

Lingerie size conversion is simpler than it looks: the number is your band size (the ribcage measurement in inches), and the letter is your cup size (the difference between your bust and band measurements). Each inch of difference equals one cup letter, starting at A for one inch. If you're between sizes or converting between systems, knowing your sister sizes can help you find a comfortable alternative.

Bra shopping can feel like deciphering a secret code, especially when you see sizes like 34B, 36C, or 32DD. But once you understand what the numbers and letters actually mean, finding the right fit becomes much easier. This guide answers common questions about lingerie size conversion, bra size letters, cup size meaning, and band size, so you can shop online or in-store with confidence.

Whether you're switching between US, UK, EU, or FR sizing, or just trying to figure out why your current bra doesn't feel right, the key is knowing your measurements and how they translate to band and cup letters. We'll also cover bra sister sizes, a handy trick for when your exact size isn't available.

What do the number and letter in a bra size mean?

The number in a bra size (e.g., 34, 36) is your band size, which corresponds to the measurement around your ribcage, just under your bust. It's usually measured in inches in the US and UK. The letter (e.g., A, B, C) is your cup size, which represents the volume of your breasts relative to your band. Cup size is not static; it changes with band size. For example, a 34B and a 36A have different cup volumes even though the letters differ.

Understanding this relationship is crucial because a bra that fits well in the band but gaps in the cup might mean you need a different cup letter, not a different band. Conversely, if the band rides up, you might need a smaller band size, which could also change your cup letter.

• Band size is measured snugly around your ribcage, rounded to the nearest even number.
• Cup size is determined by subtracting your band measurement from your bust measurement.

How do I convert my bra size between US, UK, EU, and FR sizes?

Conversion between sizing systems can be confusing because cup letters are not universal. US and UK sizes often use the same band numbers but differ in cup progression: US sizes go A, B, C, D, DD, DDD, while UK sizes go A, B, C, D, DD, E, F, FF, and so on. EU sizes typically use centimeters for the band and a different cup lettering system, while FR sizes use the same band as EU but add 15 to the band number (e.g., EU 75 = FR 90).

The safest approach is to always check the brand's specific size chart, as there can be variations. If you're shopping from a brand like FIT FULLY YOURS LINGERIE (CANADA), which uses US sizing, you'll want to convert your UK or EU size accordingly. For example, a UK 34E is roughly a US 34DDD, and an EU 75C is approximately a US 34C.

• US and UK cup letters diverge after DD; UK uses E, F, FF, etc.
• EU band sizes are in centimeters; FR band size is EU band + 15.

What is the difference between cup sizes?

Cup size indicates the volume of the bra cup, but it's relative to the band. The difference between your bust and band measurements determines your cup letter: 1 inch = A, 2 inches = B, 3 inches = C, 4 inches = D, 5 inches = DD, and so on. This means a 34B and a 36B do not have the same cup volume; the 36B cup is larger because the band is longer, and the cup is scaled proportionally.

If you're unsure about your cup size, try a bra like the B1007 Misty Soft-Cup Wireless: FAWN, which offers seamless cups and light foam padding for a natural shape. It's a good starting point for those who want a smooth look under t-shirts. Remember, cup size is not a measure of breast size alone; it's a ratio.

• Cup letter = bust measurement minus band measurement (in inches).
• A 34C and 36B are sister sizes with similar cup volume.

What are bra sister sizes and how do I use them?

Sister sizes are alternate bra sizes that have the same cup volume but different band lengths. To find a sister size, go up one band size and down one cup letter, or down one band size and up one cup letter. For example, if you wear a 34C, your sister sizes are 32D and 36B. This is useful when your exact size is sold out or if you're between band sizes.

Keep in mind that sister sizes are not a perfect substitute; the band will fit differently. If you usually wear a 34C but find the band too tight, a 36B might be more comfortable, but you may need to adjust the straps. Always check the brand's fit notes and return policy if you're unsure.

• Sister sizes share cup volume but not band length.
• Use sister sizes as a guide, not a guaranteed fit.

How do I measure my band and cup size at home?

To measure your band size, wrap a soft measuring tape snugly around your ribcage, just under your bust, and round to the nearest even number. For your bust size, measure around the fullest part of your bust, keeping the tape parallel to the floor. Subtract your band measurement from your bust measurement to find your cup size. For example, if your band is 34 inches and your bust is 37 inches, the difference is 3 inches, which equals a C cup, making you a 34C.

For accuracy, measure yourself in a non-padded bra or braless, and consider having someone help you. If you're between sizes, it's often better to go with the larger band and adjust the cups, or try a style like the B2761 Serena Lace: NAVY, which features J-hooks for adjustable support and a delicate lace design.

• Measure band snug, bust loose; keep tape level.
• If between cup sizes, try both and see which feels better.

Why does my bra size seem to change between brands?

Bra sizing is not standardized across brands, so a 34B in one brand might feel like a 34B in another but fit differently due to variations in cup shape, band elasticity, and fabric. For instance, a moulded cup bra like the B1212 Zora Moulded: FAWN offers full coverage and soft underwire cups, but its fit may differ from a lace bra like the B2645 Bridget: MAUVE PLUM, which has an inside sling for lift. Always check the brand's size chart and read reviews about fit.

If you're shopping online, look for brands that offer detailed fit guides and easy returns. FIT FULLY YOURS LINGERIE (CANADA) provides specific product descriptions and sizing options, so you can make an informed choice. When in doubt, order two sizes and return the one that doesn't work.

• Brand sizing can vary; always consult the specific size chart.
• Fabric and construction affect fit; moulded cups fit differently than unlined lace.

Bra sizing FAQ: quick answers to common questions

What if I'm between band sizes?

If your underbust measures 33 inches, you're between a 32 and 34 band. Try both; a 32 may feel tight initially but will stretch, while a 34 may ride up. Use the sister size rule: if you usually wear a 34B, try a 36A or 32C. Choose the band that feels snug but not uncomfortable; you should be able to fit two fingers under the band.

How do I know if my cup size is too small?

Signs include spillage over the top or sides, underwire digging into breast tissue, or the center gore not lying flat against your sternum. If you notice these, go up a cup size or try a sister size with a larger cup. A well-fitted cup should contain all breast tissue without bulging or gaping.

Can I convert my size to another country's sizing?

Yes, but it's not always exact. Use a conversion chart as a starting point, and always check the brand's specific sizing. For example, a US 34DD is roughly a UK 34DD, but a US 34DDD is a UK 34E. When in doubt, contact the brand's customer service for guidance.

Product facts to know

• B1007 Misty Soft-Cup Wireless: FAWN: Misty Smooth Wireless bra is a true companion for your daily adventures. It's seamless cups redefine practicality, making it an ideal choice for wearing under t-shirts or any outfit as it effortlessly vanishes under fabric. Crafted with meticulous attention to detail, this bra's light foam padding achieves a natural shape, creating an understated, yet flattering look while offering exceptional lift and support. If you prefer a wireless bra that disappears under clothing and provides a natural shape, this is a great option. It's available in cup sizes, so you can find your fit based on your band and cup measurements.
• B2761 Serena Lace: NAVY: The Serena Collection is a stunning lace set that emanates elegance and allure. This gorgeous bra with J-hooks and perfectly complementing panties available in both bikini and brief styles combines comfort and sophistication creating an unforgettable lingerie experience. Crafted with meticulous attention to detail showcases delicate lace patterns that caress the contours of the bust. The J-hooks allow you to convert the bra to a racerback, which can help if your straps slip. The lace design is beautiful for special occasions, but the fit may be less forgiving than a moulded cup, so ensure your size is accurate.

Understanding lingerie size conversion, band and cup letters, and sister sizes takes the guesswork out of bra shopping. Measure yourself regularly, consult brand-specific charts, and don't be afraid to try sister sizes when your exact size isn't available. With these tips, you can find bras that fit comfortably and look great, no matter where you shop.