Bra Size Calculator
Two measurements is all it takes. Enter your underband and bust and we'll work out your band, cup and sister sizes, plus how they convert to UK and EU. It's a starting point, not a rule, because fit varies by brand and style.
Your estimated size
—
Sister sizes to try
Same cup volume, different band. If the band feels tight or loose, these fit the same bust.
| US | — |
|---|---|
| UK | — |
| EU | — |
Cup letters and fit vary by brand and region, so treat this as a starting point and try a sister size if the band or cup feels off.
How to measure
-
Step 1
Underband
Wearing an unpadded bra or none, run the tape snugly around your ribcage directly under your bust, level all the way round. That number is your band.
-
Step 2
Bust
Keep the tape level and measure around the fullest part of your bust, without pulling tight. Standing straight gives the truest reading.
-
Step 3
Calculate
Enter both above. The difference between bust and band sets the cup; the band is your rib measurement rounded to an even number.
Cup size chart (by bust minus band)
| Difference | US cup | UK cup | EU cup |
|---|---|---|---|
| 1 in / 2.5 cm | A | A | A |
| 2 in / 5 cm | B | B | B |
| 3 in / 7.5 cm | C | C | C |
| 4 in / 10 cm | D | D | D |
| 5 in / 12.5 cm | DD / E | DD | E |
| 6 in / 15 cm | DDD / F | E | F |
| 7 in / 18 cm | G | F | G |
| 8 in / 20 cm | H | FF | H |
Band numbers are the same in US and UK (30, 32, 34…). EU bands run 65, 70, 75, 80… Above a D cup the letters diverge by region, which is why a good bra fit often means trying a sister size.
Bra size questions
What are sister sizes?
Sister sizes hold the same cup volume across neighbouring bands. Go down a band and up a cup (34C to 32D), or up a band and down a cup (34C to 36B). If your usual size fits in the cup but not the band, a sister size often solves it.
My band measurement is an odd number. What do I do?
Bands come in even numbers, so round to the nearest even one. If you're right between two, try the smaller band first for support and use a sister size if it digs in.
Why does my calculated size differ from what I usually wear?
Brands cut differently and the old "add four inches" method inflated band sizes for years. A snug band with the right cup usually feels better than a loose band a size or two up. Try your calculated size and its sisters.
How do I convert to UK or EU sizing?
The band number stays the same for US and UK; EU uses 65, 70, 75 and so on. Cup letters match up to D, then differ, so check the chart above and lean on sister sizes.
How often should I remeasure?
Every six to twelve months, and after any weight change, pregnancy or a new workout routine. Bands also stretch with wear, so a band that has crept up your back is a sign to remeasure.
Now find your fit
Your measurements help with more than bras. Shop pieces cut to flatter every shape.