Bra Size Calculator
Estimate your US bra size from two measurements: the band (underbust) and the bust (overbust). The result is a starting point — real fit varies by brand and style.
Your measurements
Brands and cuts differ, so treat this as a starting point. If the band rides up or the cup gapes, try a sister size or a different style.
How to use this calculator
1. Pick your unit
Switch between inches and centimetres. The calculator converts your measurements to inches internally, since US bra sizing is built around inch differences.
2. Measure the band (underbust)
Wrap the tape around your ribcage directly under the bust. Keep it snug and level — this becomes your band number.
3. Measure the bust (overbust)
Measure around the fullest part of the bust without compressing it. The cup letter comes from how much larger this is than the band.
4. Read the size and sister sizes
You get a band + cup size (such as 30F) and a couple of sister sizes — same cup volume, different band — to try if the fit is slightly off.
About bra sizing
How do I measure for a bra size?
The band comes from your underbust measurement and the cup from the difference between bust and band — roughly one inch of difference per cup letter. We round the underbust to the nearest whole inch and up to the next even number, the modern "round to nearest even" approach (older guides added 4–5 inches instead).
Why does it vary by brand?
There is no single global standard. US, UK, and EU systems label cups differently, and even within one country two brands can fit a full cup apart. Use a measured size to start, then fine-tune by trying bras on.
What are sister sizes?
Sister sizes share cup volume but change the band: down a band and up a cup (34C → 32D), or up a band and down a cup (34C → 36B). Handy when your usual size feels off or is sold out.