Find Your Perfect
Bra Size
Enter your band and bust measurements to get your exact US bra size — plus convert to UK, EU, or AUS sizing instantly.
Wrap a tape around your ribcage, just under your bust. Round to the nearest even number.
Measure around the fullest part of your chest, keeping the tape parallel to the ground.
The difference between bust and band determines your cup size. Enter both below →
Bra Size Converter
Convert between US, UK, EU, and Australian sizing systems in one click.
Accurate measurements are everything. Follow these four steps for the best fit.
Use a soft tape measure
A flexible seamstress tape gives far more accurate results than a rigid ruler or string-and-ruler method.
Measure without a bra
Or wear a non-padded, unlined bra. Padding adds volume and skews the bust measurement.
Keep the tape level
The tape should run parallel to the floor all the way around — front and back at the same height.
Breathe naturally
Don't hold your breath or suck in. Measure while relaxed for the most accurate band and bust reading.
| US Band | UK Band | EU Band | AUS Band | Cup Letters |
|---|---|---|---|---|
| 28 | 28 | 60 | 8 | AA · A · B · C · D · DD |
| 30 | 30 | 65 | 10 | AA · A · B · C · D · DD · E |
| 32 | 32 | 70 | 12 | AA · A · B · C · D · DD · E · F |
| 34 | 34 | 75 | 14 | A · B · C · D · DD · E · F · G |
| 36 | 36 | 80 | 16 | A · B · C · D · DD · E · F · G · H |
| 38 | 38 | 85 | 18 | A · B · C · D · DD · E · F · G · H |
| 40 | 40 | 90 | 20 | B · C · D · DD · E · F · G · H |
| 42 | 42 | 95 | 22 | B · C · D · DD · E · F · G · H |
| 44 | 44 | 100 | 24 | C · D · DD · E · F · G · H |
| EU / FR Band | US / UK Band | IT Band | Cup Comparison |
|---|---|---|---|
| 60 | 28 | 0 | A(EU) = A(US/UK) |
| 65 | 30 | 1 | B(EU) = B(US/UK) |
| 70 | 32 | 2 | C(EU) = C(US/UK) |
| 75 | 34 | 3 | D(EU) = D(US/UK) |
| 80 | 36 | 4 | E(EU) = DD(US) |
| 85 | 38 | 5 | F(EU) = DDD/E(US) |
| 90 | 40 | 6 | G(EU) = F(US) |
| 95 | 42 | 7 | H(EU) = G(US) |
| 100 | 44 | 8 | I(EU) = H(US) |
| Difference (in) | US/UK Cup | EU Cup | FR Cup | IT Cup |
|---|---|---|---|---|
| < 1" | AA | AA | AA | AA |
| 1" | A | A | A | A |
| 2" | B | B | B | B |
| 3" | C | C | C | C |
| 4" | D | D | D | D |
| 5" | DD / E | E | E | E |
| 6" | DDD / F | F | F | F |
| 7" | G | G | G | G |
| 8" | H | H | H | H |
Band rides up: The band should sit level around your body. If it rides up your back, the band is too large.
Straps dig in: Only about 10% of support should come from straps. If they're digging in, your band is doing too little work.
Cup overflow or gaps: Overflow means you need a larger cup; gaping means smaller. The cup should fully contain the breast.
Centre gore doesn't lie flat: The centre panel between cups should touch your sternum. If it doesn't, go up a cup size.
Sister sizes share the same cup volume but differ in band size. Moving up a band and down a cup — or vice versa — gives the same breast volume with a different fit feeling.
Example: 34C, 36B, and 32D all have the same cup volume. If 34C feels tight in the band, try 36B for the same coverage with more comfort.
Sister sizing is especially useful when your calculated size isn't available or feels inconsistent across brands.
Bra Size Calculator — Find Your Perfect Fit
Finding the right bra size can be surprisingly difficult. Studies suggest that up to 80% of women wear the wrong bra size — either too tight in the band, too small in the cup, or both. The right fit provides proper support, prevents discomfort, and significantly improves posture and confidence.
Our free bra size calculator takes two simple measurements — your band size (underbust circumference) and your bust size (fullest chest circumference) — and instantly calculates your correct US bra size along with sister size recommendations. The built-in converter also handles US, UK, EU, and Australian sizing systems, so you're covered no matter which brand or region you're shopping in.
Use the calculator above, then read the guides below to understand what the results mean, how to ensure the best fit, and when to remeasure.
How Bra Sizes Are Calculated
Bra sizing has two components: the band size (a number) and the cup size (a letter). The band number represents your ribcage circumference in inches, rounded to the nearest even number. The cup letter represents the difference between your bust measurement and your band measurement.
The Cup Size Formula
< 1" difference → AA cup
1" → A cup | 2" → B cup | 3" → C cup
4" → D cup | 5" → DD cup | 6" → DDD/F cup
7" → G cup | 8" → H cup | 9" → I cup
Band Size Rounding Rule
Band sizes are always even numbers. If your underbust measurement is an odd number (e.g., 33"), round up to the nearest even number (34"). If you measure exactly on an even number, try both that size and the next size down to find what feels most secure and comfortable.
What "True" vs "Vanity" Sizing Means
Some older sizing guides used a "+4 rule" (adding 4 inches to an odd band measurement, or +2 to an even one) to account for less stretchy fabrics in older bras. Modern bras use far more elastic materials, so most fitters now recommend measuring your actual underbust circumference without the addition. Our calculator uses the modern direct measurement method.
Step-by-Step Measurement Guide
Accurate measurements are the foundation of a good fit. Even a half-inch error in your band measurement can shift you an entire band size. Follow these steps carefully:
Step 1 — Measure Your Band Size
Wrap a soft tape measure snugly around your ribcage, directly beneath your bust. The tape should be level all the way around — not tilting up at the back. Breathe normally. Note the measurement in inches, then round to the nearest even number. This is your band size.
Step 2 — Measure Your Bust Size
With either no bra or a non-padded, unlined bra, wrap the tape around the fullest part of your chest, usually across the nipple line. Keep the tape parallel to the floor — it should not dip in the back. Write down this measurement to the nearest half inch.
Step 3 — Calculate the Difference
Subtract your band measurement from your bust measurement. The result (in inches) maps directly to your cup size using the table above. Enter both measurements into the calculator and it will do this automatically.
Tips for the Most Accurate Result
Lean forward slightly when measuring the bust — this allows breast tissue to fall naturally into cup position, giving a more accurate fullness reading. Do not pull the tape too tight or leave it too loose — it should lie flat against the skin without pressing in. Measure twice and average the results if you get slightly different numbers.
Understanding International Bra Sizing Systems
Bra sizing is not uniform across the world. Different regions use different numbering systems for the band and sometimes different letter progressions for cups. Here is a quick reference:
US vs UK Sizing
US and UK band sizes use the same numbers (e.g., both use 34, 36, 38). The cup letters are also mostly the same up to D, but diverge at larger sizes. US uses DD, DDD, DDDD while UK continues with E, F, FF, G. When shopping UK brands in a US context, always verify the cup letter equivalency.
EU Sizing
European (and French) bra sizing converts the band to centimeters in increments of 5. A US/UK 32 band equals an EU 70 band, a US/UK 34 equals EU 75, and so on (add 38 to the US band to get the EU equivalent approximately, or use our converter). EU cup letters also shift — EU E = US/UK DD, EU F = US/UK DDD/F.
Australian Sizing
Australian band sizes are 16 less than US sizes. A US 34 band = AUS 18 band. Cup letters are the same as US and UK. When shopping Australian brands like Berlei, Triumph AU, or Bendon, use our converter to find your correct AUS size.
Tips for Getting the Perfect Bra Fit
Even after finding your calculated size, bras can still feel off due to style, construction, and brand differences. Here are the most important fit checkpoints:
The 90/10 Support Rule
About 90% of your support should come from the band, not the straps. The band should feel snug — you should only be able to fit two fingers underneath it at most. If the band rides up or feels loose, go down a band size. If it feels too restrictive, try a sister size (same cup volume, larger band, smaller cup).
Cup Fit Checkpoints
The cup should fully encapsulate the breast with no spillage over the top or sides (overflow), and no gaps or wrinkling in the fabric (too large). The underwire (if present) should sit flat against the ribcage all the way around, not on breast tissue.
When to Size Up or Down
If the band feels fine but the cup is too small, go up one cup size (e.g., 34C → 34D). If the cup fits but the band is too loose, go down a band size and up a cup to maintain volume (e.g., 36C → 34D — a sister size). Always start adjustments one step at a time.
Wearing on the Loosest Hook
New bras should be worn on the loosest hook. As the fabric stretches over time, you can move to the middle and then the tightest hook to extend the bra's life and maintain the same fit.