Bra Size FAQ
Short answers about bra sizes: how a band should fit, how cup letters work, what sister sizes are and how to convert between US, UK, EU, French and Australian sizes. For your own size, use the calculator with your measurements; for fit, trust how the bra feels over the label.
Questions and answers
Is brasize.app free?
Yes. The calculator, converters and charts are free with no account. There is no advertising on the site at the moment. It is published by a small Swedish company, named at the bottom of every page.
Are my measurements sent anywhere?
No. All calculations run in your browser. Your last measurements are kept only in your own browser’s storage so you do not need to type them again, and the Clear button deletes them.
How should a bra band fit?
Firm and level around your ribcage, on the loosest hook when the bra is new. You should be able to slide two fingers under it. If it rides up at the back, it is usually too loose.
What are sister sizes?
Sizes with about the same cup volume on a different band: band up one and cup down one, or the reverse. 34C, 32D and 36B are sisters. They help when the cups fit but the band does not.
Is 34C the same as 32D?
They are sister sizes with about the same cup volume. The 32D has a band about two inches shorter, so it feels firmer. They are not identical, so choose by how the band feels.
What is 75C in US size?
On standard charts, an EU 75C is a US and UK 34C, a French 90C and an Australian 12C. Brands vary, so check the brand’s own chart too.
Why are UK and US sizes different after D?
Both count cups in one-inch steps but name the larger cups differently. The UK uses DD, E, F, FF, G; the US usually uses DD/E, DDD/F, G, H. A UK F is a US G.
Do I add inches to my band?
Most modern guides do not. The older method added 4 or 5 inches to the underbust and tends to give a loose band. This site rounds your snug underbust to the nearest even inch.
Why do sizes vary between brands?
Brands do not all follow one shared standard, and band stretch and cup shape differ by design. Use your calculated size as a starting point and try bras on.
How often should I measure?
Whenever a bra stops fitting well, and after body changes such as weight change, training, pregnancy or nursing. Bodies change, and so can the right size.
What if I am between sizes?
Try both, and the sister sizes. A firm band that stays level and cups without gaps or spilling matter more than the exact number on the label.
Still unsure?
Start with the calculator, read how to measure, or write to info@brasize.app.
Last updated: October 15, 2026