Two measurements. One accurate bra size.

Skip the fitting-room guesswork. Enter your underbust and bust measurements and get an instant estimate in US, UK, EU and AU/NZ sizing.

Results in under a minute, no sign-up needed
Works in inches or centimetres
Cross-references UK, EU and AU/NZ equivalents

Calculate your size

Measure with a soft tape, standing naturally, over a well-fitted (or no) bra.

Measurement unit

Underbust (rib cage)

Bust (fullest point)

Please enter both measurements as positive numbers.

Your estimated US size

How to measure yourself

Two measurements are all the calculator needs take both over light clothing or a non-padded bra for the truest reading.

Wrap the tape under your bust

Run the tape directly under your bust, around your rib cage. Keep it level and snug firm enough to stay put, not tight enough to dig in.

Measure around the fullest point

Wrap the tape around your back and across the fullest part of your bust, keeping it parallel to the floor. Breathe normally and don't pull it tight.

Enter both numbers above

The gap between the two measurements is what determines your cup size the calculator does that math for you instantly.

Tip: Measure at chest height in front of a mirror, arms relaxed at your sides. Re-measure if the tape rides up your back that's the most common source of an inaccurate reading.

Size conversion chart

Band numbers and cup letters shift between regions use this to translate a size you already know.

US	UK	EU	AU / NZ
28A	28A	60A	6A
30B	30B	65B	8B
32C	32C	70C	10C
32D	32D	70D	10D
34D	34D	75D	12D
34DD	34DD	80E	14DD
36DDD	36E	85F	16E

What the cup difference means

Subtract your underbust from your bust measurement the result in inches maps to a cup letter.

Bust minus underbust	US cup	Example size
0–1 in	AA	32AA
1–2 in	A	32A
2–3 in	B	32B
3–4 in	C	32C
4–5 in	D	32D
5–6 in	DD / E	32DD
6–7 in	DDD / F	32DDD
7–8 in	G	32G

Is your current bra actually fitting?

Your calculated size is a starting point these signs tell you whether a bra is really working for you.

Signs it fits well

The band sits level, parallel to the floor, front and back
You can slide two fingers under the band, snugly, on the loosest hook
The centre gore lies flat against your breastbone
Straps stay put without digging in or slipping off
No spilling over the top or gaping at the cup edges

Signs it's time to size up or down

The band rides up at the back within an hour of wearing
You're on the tightest hook and it's still loose
Underwire sits on breast tissue instead of around it
Straps leave red marks or need constant adjusting
Cups wrinkle or pucker where they should sit smooth

Sister sizes worth trying

Different band-cup combinations that hold roughly the same cup volume handy when your exact size runs out.

If this feels snug in the band	Try this instead	Why it works
32C	34B	Band up one size, cup down one letter same volume
34D	36C	Looser band, same cup volume, less underarm pressure
30DD	32D	Useful when a 30 band isn't stocked in your cup
36B	34C	Band down one size, cup up one letter same volume

Sister sizes are a fitting-room shortcut, not a replacement for your calculated size always try the closest match first.

Make a good fit last longer

Elastic wears out well before fabric does a little care keeps your size accurate for longer.

Hand-wash when you can

Washing machines and tumble dryers break down elastic fibres fast. A cold hand-wash, then air-dry flat, keeps the band snug for months longer.

Rotate at least two bras

Elastic needs 24 hours to recover its shape after wear. Wearing the same bra daily stretches the band out permanently, faster than expected.

Re-measure every 6–12 months

Weight changes, hormonal shifts and even the season can shift your size. Re-run the calculator periodically rather than assuming it stays fixed.

Frequently asked questions

Common questions about measuring and reading your result.

How accurate is this calculator?

It gives a reliable starting estimate based on standard sizing formulas, but fit varies by brand, fabric and style treat the result as a fitting-room starting point, not a guarantee.

Should I measure over a bra or without one?

A well-fitted, non-padded bra gives the most consistent reading. If you don't have one on hand, measuring bare with the tape snug against your skin works too.

What if I fall between two band or cup sizes?

Round the underbust measurement to the nearest whole number. If you're exactly between two sizes, try the smaller band with a larger cup first sister sizes usually fit similarly.

Why do UK and US sizes look different?

Band numbers usually match, but cup lettering diverges after a D UK sizing continues DD, E, F, while US sizing often repeats D as DD, DDD.

What are "sister sizes"?

Sizes with the same cup volume but a different band-cup combination for example, 34B and 32C. Going up a band and down a cup (or the reverse) often gives a comparable fit.

Do sizes vary between brands?

Yes, noticeably. Two brands' 34C can differ by an inch or more in cup volume, so use this result as your starting point and adjust based on how a specific brand runs.

Still unsure about your fit?

Re-measure with a friend's help for the most accurate reading, or scroll back up and try again.

Back to the calculator