What is a bra size?
A bra size is a two-part measurement consisting of a band size (numeric, based on underbust circumference) and a cup size (letter, based on the difference between bust and underbust measurements). For example, in a size 34C, the 34 represents the band measurement in inches and the C represents the cup volume — a 2 to 3 inch difference between bust and underbust. Cup letters do not represent the same volume across different band sizes; a 32D and a 38D have different actual cup volumes despite sharing a D cup letter. Always read band and cup together.
You'll measure your underbust and bust in under 5 minutes, use the interactive calculator below to get your size instantly, verify with the AA–HH cup chart and fit checks, and learn sister sizing — the single fastest fix for "close but not perfect" bras. We'll also cover what to do at every cup size, US versus UK versus EU conversion, and the common mistakes that produce poorly-fitting bras year after year.
Already Know Your Size? Shop the Right Bra
Browse bras by goal — every style, every size from AA through HH, with fit notes on each product page.
Shop All Bras → DD+ Collection →Calculate Your Bra Size
Enter your underbust and bust measurements. We'll calculate your size, give you sister sizes, and recommend the right bra style for your shape.
Based on a 34-inch underbust and 37-inch bust (3-inch difference).
A T-shirt bra or wireless contour bra is the daily-wear standard at this size.
- Bra size = band + cup: band is your underbust measurement, cup is the difference between bust and underbust.
- Measure twice: a soft tape, snug but not tight, parallel to the floor at both underbust and bust.
- Cup difference rule: 1 inch = A cup, 2 inches = B, 3 inches = C, 4 inches = D, and so on up to HH.
- Sister sizing: up one band + down one cup, or down one band + up one cup, maintains the same cup volume.
- Re-measure every 6–12 months and after any significant body change.
- The band carries 80% of support — straps should not be doing the work.
- Style matters as much as size: the right size in the wrong cut still won't fit.
Bra Size Basics: What Band and Cup Actually Mean
Your bra size is not "small/medium/large" — it's a two-part measurement combining a band number with a cup letter. When both are correct, bras feel supportive, flattering, and comfortable. When either is wrong, you get the familiar problems: spillage, gaping, riding up, digging straps, and the feeling that bras "just don't fit."
Band size (the number) is based on your underbust measurement — the circumference of your ribcage directly under the bust. Band size carries roughly 80 percent of a bra's support load. When the band is right, the bra stays anchored on your body and everything else functions correctly. When the band is wrong, the entire bra fails regardless of how good the cups are.
Cup size (the letter) is based on the difference between your bust measurement (at the fullest point) and your underbust measurement. Cup letters represent volume, not size — a 32D and a 38D have very different actual cup volumes despite sharing a D cup letter. This is why "I'm a D cup" is meaningless without the band number.
Most women are wearing the wrong bra size — usually a band that's too loose and a cup that's too small. The fix is almost always to size down on band (one or even two sizes) and up on cup to maintain volume. A snugger band feels strange at first if you're used to a loose one, but it produces dramatically better support, shape, and comfort.
How to Measure Your Bra Size in 5 Minutes
Two measurements, a soft tape measure, and 5 minutes. Best done over a non-padded bra or bare skin — measuring over thick clothing or padded bras introduces error. Take both measurements twice and average if results differ slightly.
Measure Your Underbust
Stand straight with relaxed shoulders. Wrap a soft tape measure around your ribcage directly under your bust, where the band of a bra would sit. Keep the tape parallel to the floor and snug but not tight — you should be able to take a normal breath comfortably.
Record the measurement in inches. If the number is odd (33, 35, 37), round to the nearest even number (34, 36, 38). If it's already even, that's your starting band size. Most adult women fall between band sizes 30 and 44.
Measure at the Fullest Point
Keep the tape level and wrap it around the fullest part of your bust — usually at nipple level when standing upright. The tape should be comfortably snug, not compressed. Don't pull the tape tight; the goal is the natural circumference of the breast, not a smaller-than-real number.
Record this measurement in inches. For most accuracy, measure twice and average. Common bust measurements range from 30 to 48 inches.
Subtract Underbust From Bust
Subtract your underbust measurement from your bust measurement. The difference in inches determines your cup size using the chart below. For example, a 34-inch underbust and a 37-inch bust gives a 3-inch difference, which equals a C cup. The full size is 34C.
Use the calculator above or the cup difference chart in the next section to look up your cup letter. The result is your starting size — final fit can vary by brand and style, so confirm with a fit check.
Cup Size Chart (AA to HH)
Cup letters represent volume based on the bust-minus-underbust difference. Use this chart to translate your measurements into a cup letter — the calculator above does this automatically, but the chart is useful for understanding the system.
| Difference (inches) | Cup Size (US) | Cup Size (UK) | Cup Size (EU) |
|---|---|---|---|
| 0 – ½" | AA | AA | AA |
| ½ – 1" | A | A | A |
| 1 – 2" | B | B | B |
| 2 – 3" | C | C | C |
| 3 – 4" | D | D | D |
| 4 – 5" | DD / E | DD | E |
| 5 – 6" | DDD / F | E | F |
| 6 – 7" | G | F | G |
| 7 – 8" | H | FF | H |
| 8 – 9" | HH | G | — |
| 9 – 10" | I | GG | I |
| 10 – 11" | J | H | J |
A 32D, a 36D, and a 40D all have different actual cup volumes despite sharing the same cup letter. As band size increases, cup volume at the same letter also increases. This is why two friends who are both "D cups" can have visibly different bust sizes — the band number changes everything.
Sister Sizes: The Fastest Way to Fix a "Close But Not Perfect" Bra
Sister sizing is the single most useful concept in bra fitting. The rule: go up one band size and down one cup letter, or go down one band size and up one cup letter, to maintain the same cup volume. This solves the most common fit problem — cups fit but the band doesn't, or vice versa.
For example, a 34C has two sister sizes: 32D (smaller band, larger cup letter) and 36B (larger band, smaller cup letter). All three have approximately the same cup volume but different band tension. If your 34C feels snug at the band but the cups fit, try 36B. If the 34C feels loose at the band but the cups fit, try 32D.
| Your Current Size | Band Too Tight? Try | Band Too Loose? Try |
|---|---|---|
| 32B | 34A | 30C |
| 34C | 36B | 32D |
| 36D | 38C | 34DD |
| 34DD | 36D | 32DDD |
| 38DD | 40D | 36DDD |
| 36G | 38FF | 34GG |
| 40D | 42C | 38DD |
The 5-Point Fit Check (Confirm Your Size)
Calculated size is a starting point, not a guarantee of fit. Brand variance means the same numeric size can fit differently across different brands. Use this 5-point check on every bra you try on to verify the size and shape match your body.
From the side, the band should sit at the same height in front and back — perfectly horizontal across the body. If it rides up between your shoulder blades, the band is too loose. Sister down (smaller band + larger cup letter) to fix.
You should fit two fingers (snugly) under the band at the back — not a whole hand, not zero fingers. The band should feel firm but not painful. Always buy on the loosest hook so you can tighten as elastic stretches.
No spillage at the top, sides, or center. No gaping or wrinkling at the upper cup edge. If you have spillage, sister up. If you have gaping, try a different cup style (plunge, demi, unlined) before changing size — gaping is usually a shape mismatch.
For wired bras, the center gore between the cups should press flush against the sternum with no visible gap. If you can see space when looking down, the band is too loose or the cup is too small. Sister down usually fixes it.
Straps should support without carrying the weight. If they dig into your shoulders, the band is doing too little. Loosen the straps until they're just snug — if the bust drops, fix the band. Strap digging is almost always a band problem.
Raise your arms, twist side to side, and bend forward. The cups should not shift, spill, or expose tissue. The band should stay in place. If anything moves significantly, the size is wrong — typically the band is too loose.
"Most women evaluate bras by cup feel and skip the band check entirely. But a loose band makes every other element fail — cups slide forward, gore floats off the sternum, straps take over, and the bust drops by hour three. Always start with the band."
— HauteFlair Fit Editorial Team
Cup-by-Cup Guide: What Each Size Typically Needs
Different cup sizes have different fit priorities, common challenges, and best-style matches. Use this guide to refine your shopping by your actual size.
Smaller Bust — Shape and Light Support
AA and A cups typically benefit from shape plus light support. Unlined and wireless styles can be surprisingly flattering and comfortable. For visible enhancement, push-up plunge bras work effectively at this cup range — the smaller volume tolerates added foam without spillage. For smooth daily wear, lightly padded T-shirt bras reduce nipple show-through under fitted tops.
Common issue at AA/A: cup gaping with rigid molded cups. Fix: choose plunge, demi, or unlined cups that conform to your shape rather than forcing tissue into a fixed mold.
Versatile Range — Most Styles Work
B and C cups have the most styling flexibility. T-shirt bras smooth under fitted clothing. Plunge bras work for V-necks. Lightly padded molded cups add polished daily shape. Push-up styles work at B (less reliably at C — some women find them comfortable, others get top-edge spillage).
Common issue at B/C: gaping at the top edge of full-coverage cups due to upper-light tissue distribution. Fix: try plunge or demi cups (lower upper edge), or choose a brand whose cup pattern matches your tissue distribution.
Structure Starts to Matter
D and DD cups need bras with structure — supportive bands, stable cups, and side panels that contain tissue properly. Full-coverage molded bras are the daily standard. T-shirt bras work for fitted clothing. Plunge bras work for V-necks but choose full-coverage plunge, not light plunge, at this cup range. Skip heavy push-up — combined volume causes top-edge spillage.
Common issue at D/DD: incorrect band size makes everything worse. Many women labeled "D" are actually wearing too-loose bands. Sister down (e.g., from 36D to 34DD) often produces dramatic comfort improvement.
Full-Bust Construction Required
DDD and above need bras specifically engineered for full bust support. Look for full-bust specialty brands (Panache, Wacoal, Curvy Kate, Elomi, Freya, Goddess) that build with reinforced side panels, structured cups, heavier-gauge wires, and wide bands. Generalist brands typically can't deliver proper support at this cup range, even if they list the size.
Common issue at DDD+: shopping by cup letter alone. A "DDD" bra from a generalist brand differs substantially from a "DDD" from a full-bust specialty brand — the construction principles differ. Always check the brand's intended size range.
Shop: DD+ Collection · Full-Figure Bras · Minimizer Bras.
US, UK, and European Size Conversion
Cup sizing diverges between systems above D. Below D, US, UK, and EU sizing is similar. From DD upward, the labels shift — a US DDD is UK E and EU F. Use this chart when shopping international brands.
| US Cup | UK Cup | EU Cup | Difference (in) |
|---|---|---|---|
| A | A | A | ½ – 1" |
| B | B | B | 1 – 2" |
| C | C | C | 2 – 3" |
| D | D | D | 3 – 4" |
| DD / E | DD | E | 4 – 5" |
| DDD / F | E | F | 5 – 6" |
| G | F | G | 6 – 7" |
| H | FF | H | 7 – 8" |
| I | G | I | 8 – 9" |
| J | GG | J | 9 – 10" |
| K | H | — | 10 – 11" |
| L | HH | — | 11 – 12" |
Band sizes are measured the same way internationally but labeled differently. A US 32 band ≈ UK 32 ≈ EU 70. A US 34 ≈ UK 34 ≈ EU 75. A US 36 ≈ UK 36 ≈ EU 80. When shopping international brands, check the brand's specific size chart — there's slight variation between conversion systems.
Shop by Need: Picking the Right Style
The right size in the wrong style still won't fit well. Match style to your primary goal:
If you only buy one bra after re-measuring, make it a molded T-shirt bra in your new size. The smooth molded cup is the most forgiving — it works under most outfits, reduces nipple show-through, and gives you a clean reference fit to compare other styles against. Most women's daily-wear bra rotation includes 2 to 3 T-shirt bras as the foundation.
Frequently Asked Questions
What is a bra size?
How do I measure my bra size at home?
What is the difference between AA, A, B, C, D and larger cup sizes?
What is sister sizing?
How do I know if my bra fits correctly?
How often should I re-measure my bra size?
What if I'm between two band sizes?
What if I'm between two cup sizes?
Why do my straps dig into my shoulders?
What size am I in UK or European cup sizes?
Do bra sizes change with weight loss or gain?
How do I measure my bra size without a tape measure?
What does 34C actually mean?
Is DD the same as E cup?
What is the most common bra size?
This guide is editorial. Bra sizing varies by brand, fabric, and design — measurements are a starting point and should be confirmed with fit checks. When a product page includes a specific brand sizing note, follow that first. For deeper guides on individual cup sizes and bra styles, see our fit guide and bra type taxonomy. Last updated: May 11, 2026.
