How to Measure Your Bra Size
Two measurements, a soft tape, and about five minutes. Here is exactly where the tape goes, how to read the numbers, and how to turn them into a band and cup size.
Last reviewed on 28 April 2026.
A bra size is two numbers in disguise. The band comes from the measurement around your ribcage, and the cup comes from how much bigger your bust is than that ribcage measurement. Get those two measurements right and the rest is arithmetic — which the calculator does for you. You only need a soft cloth measuring tape (the kind used for sewing); if you only have a rigid tape, a piece of string you mark and lay flat against a ruler works too.
Step 1 — Measure your underbust (band)
Wrap the tape around your ribcage directly under your bust, where the band of a bra sits. Keep it level all the way around — same height at the front and the back — and parallel to the floor. Pull it snug, firm enough that it would not slide down, but not so tight that it bites. Breathe out normally and read the number. Round to the nearest whole inch (or centimeter).
That underbust number is your band size. Bands are made in even numbers, so the calculator rounds to the nearest even band for you. If you measure an odd number, you sit between two bands — more on that in the FAQ below.
Step 2 — Measure your full bust
Now wrap the tape around the fullest part of your bust — usually across the nipple line. Keep it level front to back and do not pull tight; the tape should rest against the tissue without compressing it. Stand normally and read the number. For the most reliable result, measure over a thin, non-padded bra or no bra at all. A padded or push-up bra changes the shape and inflates the number.
Step 3 — Turn the numbers into a size
Subtract your underbust from your full bust. The difference, in inches, gives the cup letter — roughly one inch per letter. The table below shows the standard mapping (and how the same cup is labelled in the UK and EU, which diverge once you pass D).
| Bust − Underbust | US cup | UK cup | EU cup |
|---|---|---|---|
| 0 in | AA | AA | AA |
| 1 in | A | A | A |
| 2 in | B | B | B |
| 3 in | C | C | C |
| 4 in | D | D | D |
| 5 in | DD | DD | E |
| 6 in | DDD / F | E | F |
| 7 in | G | F | G |
| 8 in | H | FF | H |
So a 34-inch underbust with a 38-inch bust is a 4-inch difference — a 34D. The same 4-inch difference on a 30-inch underbust is a 30D; the letter is the same but the actual cup is smaller, because the body underneath it is smaller. That is why a cup letter on its own never tells you much without its band.
Have your two numbers? Let the calculator do the rest.
Calculate My SizeMistakes that throw the numbers off
- Measuring over a padded bra. Padding adds inches to the bust measurement and pushes the cup result too large. Measure over something thin or nothing at all.
- A loose underbust tape. The band measurement should be firm. A tape that sags reads too big and lands you in a band that will ride up.
- An uneven tape. If the tape rides higher at the back than the front, both numbers drift. Check it in a mirror.
- Holding your breath. Breathe out normally for the band measurement — puffing your chest out adds an inch you do not wear.
For a fuller list of what goes wrong and how to spot it, see common bra measuring mistakes.
After you have a size
Treat your calculated size as a starting point, not a verdict. Real bras vary by brand and cut, so the best fit is often your calculated size or one of its sister sizes — the same cup volume on a tighter or looser band. When you try a bra on, run through the fit test: the band should sit level, the centre should tack flat against your sternum, and the cup should hold the tissue without gaps or spillage. You can also open the guide for your exact size from the size index to see its measurements, conversions, and fit notes.
Frequently asked questions
Should I measure with a bra on or off?
Measure your underbust directly against your skin or over a thin, non-padded bra. Measure your full bust over a thin, non-padded bra — a wired push-up or padded bra distorts the number. A soft, unlined bralette or no bra at all gives the most reliable bust measurement.
What if my measurement falls between two band sizes?
Bands come in even numbers. If your underbust lands on an odd number or between sizes, try the size each way: the smaller band gives firmer support, the larger band more comfort. Because the band stretches with wear, many fitters suggest starting with the snugger option.
Can I measure my bra size in centimeters?
Yes. Take both measurements in centimeters and switch the calculator to CM. The method is identical — the calculator handles the conversion and returns US, UK, EU, FR, AU, and JP sizes.