How do I measure for a bra?

BAND: wear thin non-padded bra or no bra. Measure underbust circumference snugly around ribcage just below breasts, tape level all around. Pull snug but not constricting. BUST: measure around fullest part of breasts (typically nipple level), tape level, comfortable. Both in inches. Calculate: if underbust odd number, round up to even for band size. Subtract band from bust: 0"=AA, 1"=A, 2"=B, 3"=C, 4"=D, 5"=DD, 6"=DDD/F, etc. Use this as starting point; try on for actual fit. For accuracy: measure 2-3 times; ideally not pregnant, not menstruating (size fluctuates).

What does the band number mean?

Band number represents ribcage circumference in inches. 32 band = roughly 32" ribcage (with adjustments for fit). Band carries 90% of bra's support; should fit snugly with two fingers space horizontally. Should be horizontal in back, not riding up — if band rides up, it's too loose. If digging or causing discomfort, too tight. Even numbers standard (32, 34, 36, 38, 40, 42, 44, 46). Some specialty brands offer 28, 30 (for smaller frames) and 48+ (for larger frames). Specialty fitters often suggest going DOWN one band size from measurement; ribcage stretches band slightly more than it appears.

What is a sister size?

Sister sizes have same cup VOLUME but different band/cup combinations. Moving up one band size: decrease cup letter by one for same volume. Moving down: increase cup letter. Example: 32D = 30DD = 34C = 36B = 38A (same cup volume). 34C = 32D = 36B (same volume). Useful when: (1) Between sizes — try sister-size. (2) Brand doesn't carry your exact size — try sister-size in available range. (3) Want different look — same volume, different fit (smaller band = tighter band fit). (4) Adjusting for fit issues — band rides up: try sister-size DOWN in band, UP in cup.

Why does my bra size keep changing?

Many reasons: WEIGHT CHANGES — even 5-10 lb shifts affect breast tissue, ribcage. HORMONAL CHANGES — menstrual cycle, birth control, menopause, hormone therapy. PREGNANCY — significant growth, expanding ribcage. NURSING — establishing milk supply, weaning. AGING — tissue density changes; ribcage expansion. SURGERY — breast augmentation, reduction, mastectomy. BAND STRETCHING — bras lose elasticity over time, leading you to fasten on tighter hooks; eventually replace. PHYSICAL TRAINING — significant muscle development changes ribcage. EMOTIONAL stress — fluid retention. Most women need re-fitting every 1-2 years; more often during life transitions. Old bras shouldn't be reference for current fit.

How do I know if my bra fits correctly?

Key checks: BAND — horizontal in back (not riding up), comfortable but firm, can slip 2 fingers under. CUPS — smoothly cover breast with no gaps or overflow; underwire sits flat against ribcage outside breast tissue. STRAPS — adjustable, comfortable; not digging in, not slipping; carrying maybe 10-20% of weight (rest by band). CENTER GORE (front of band) — sits flat against breastbone, not lifting away. NO SPILLAGE — neither at top of cup (quad-boob) nor sides/armpits. STRAIGHT POSTURE — bra doesn't pinch or restrict breathing. Comfortable to wear all day. If any of these fail: try different size, style, or brand. Don't accept discomfort — proper fit eliminates most bra-related problems.

Bra Size Calculator

Find your correct bra size by entering your underbust (band) and bust measurements. The calculator determines your band size and cup size based on the difference between these two measurements.

Bra fitting is notoriously difficult, with industry research consistently finding that 70-80% of women wear the wrong bra size. The combination of complex measurement systems, brand variations, and lack of fitting expertise creates persistent fitting problems. Wearing the wrong bra size causes daily discomfort, back and neck pain, poor posture, breast tissue migration over time, and unflattering appearance. Getting the right size matters more than most consumer products because bras directly affect comfort, health, and appearance.

The traditional sizing method (subtract band from bust, each inch difference = one cup size) provides starting estimates but often fails in practice. Brand variations dramatically affect actual fit — a 34C in one brand may be 32D in another, 36B in a third. Different breast shapes (full on top, full on bottom, projected, wide-set) all fit specific styles better, regardless of "correct" size. Professional bra fitting at specialty stores (Nordstrom, specialty boutiques) helps many women find their correct size for the first time — often dramatically different from what they've been wearing.

This calculator provides starting size estimates from underbust and bust measurements. Use it for: initial bra fitting guidance, online bra shopping, sister-size finding (same volume, different band/cup), or learning sizing fundamentals. Important context: this is starting point only. ACTUAL FIT requires trying on and assessing: band horizontal in back (not riding up), straps not digging or slipping, cups smoothly covering breast without gaping or overflow, center gore (front of band) flat against breastbone. Different bra styles (T-shirt, balcony, plunge, full-coverage) fit differently even at same size. Many women find professional fittings transformative. For nursing, post-pregnancy, post-mastectomy, or significant weight change, re-fitting essential as size changes substantially.

Inputs

Underbust / Band (inches)

Measure snugly around ribcage, just below the bust

Bust (inches)

Measure around the fullest part of the bust

Results

Your Bra Size

32D

Band Size

Cup Size

Size Details

Detail	Value
Underbust Measurement	32 inches
Bust Measurement	36 inches
Band Size	32
Bust-Band Difference	4.0 inches
Cup Size	D
Your Size	32D
Sister Size (band up)	34C
Sister Size (band down)	30DD

Last updated: May 27, 2026

Formula

Standard bra sizing: Step 1: Band size Measure underbust circumference in inches (snug, level) If odd number: round up to next even number This is your band size (32, 34, 36, etc.) Some methods add 0-4 inches to underbust for band size (older "+4 method"). Modern fitting often skips this addition — uses underbust directly or rounds up to nearest even number. Step 2: Cup size Measure bust at fullest point Difference (bust - band) determines cup size: 0" = AA 1" = A 2" = B 3" = C 4" = D 5" = DD/E 6" = DDD/F 7" = G 8" = H 9" = I 10" = J Example: Underbust 32", bust 36". Band: 32 Difference: 4 inches → cup size D Initial size: 32D Modern note: some women in 32 band measurement test better in 30 band; "tight band" approach used by specialty fitters. Cup size letters by region: US/UK letters somewhat aligned, but US uses double-letter system, UK uses different progression: US: AA, A, B, C, D, DD, DDD, G, H, I, J... UK: AA, A, B, C, D, DD, E, F, G, GG, H, HH, J, JJ... EU: AA, A, B, C, D, E, F, G, H... UK D+ uses single-letter progression. US DD = UK DD = EU E. Conversion approximate (US/UK): US C = UK C US D = UK D US DD = UK DD US DDD/F = UK E (after this, systems diverge significantly) US G = UK FF US H = UK G US I = UK GG US J = UK H Band size conversion: US: 28, 30, 32, 34, 36, 38, 40, 42, 44, 46 UK: 28, 30, 32, 34, 36, 38, 40, 42, 44, 46 EU/AU: 60, 65, 70, 75, 80, 85, 90, 95, 100, 105 JP: same numbers as US Standard US 34 = UK 34 = EU 75. Sometimes slight differences. Sister sizes: Same cup volume, different band/cup combinations. Moving up one band size: go down one cup size for same volume. Moving down one band size: go up one cup size. Example sister sizes (same cup volume): 30D = 32C = 34B = 36A 32D = 34C = 36B = 38A 32DD = 34D = 36C = 38B 36D = 38C = 40B Useful when: - Between band sizes (try sister size) - Brand doesn't carry your exact size - Want different look/feel - Adjusting for fit issues Common fit issues: Band riding up in back: Band too loose; try smaller band Sister-size up in cup if cup fits Straps digging: Band too loose; cups doing too much work Smaller band, larger cup Quad-boob (overflow at top of cup): Cup too small; try larger cup Same band, larger cup Cup gaps: Cup too big; try smaller cup Possible breast shape mismatch with style Center gore (front band) lifts away: Band too loose OR cup too small (forcing gore out) Try smaller band first, then larger cup Underwire poking: Wrong size, shape, or style Should sit flat against ribcage outside breast tissue Sliding straps: Wide-set straps may not work with narrow shoulders Try different style or convertible straps Breast shape considerations: Full on top: more volume above nipple Plunge, balconette work well Avoid full coverage that gaps Full on bottom: more volume below nipple Demi cup, balconette Avoid styles requiring fullness at top Projected (deeper, narrower): forward projection Plunge bras Avoid wide-set cups Wide-set: breasts far apart Wide-set cups Avoid plunge styles Shallow: breasts close to chest wall Lighter padding for shape Avoid push-up styles (uncomfortable) Asymmetric (common): one breast larger than other Choose size based on larger breast Removable padding in smaller cup Choosing size when between: If between band sizes: Generally go with smaller (band stretches over time) Or sister-size up in cup If between cup sizes: Smaller cup if borderline Larger if pressing into tissue Brand-specific variations: Victoria's Secret: generally runs small (size up 1) Aerie: relatively true-to-size Calvin Klein: tends to fit smaller ThirdLove: extended sizes including half-cups True&Co: focus on fit measurement Cuup: bralette-focused Wacoal: full-coverage, often runs larger Each brand's "size 34D" fits differently. Cross-reference brand-specific size charts. Specialty bra types: Sports bras: extra support; sized different from regular T-shirt: smooth contour; no visible seams Balconette/balcony: lower coverage; emphasizes décolletage Demi: half cup; for fuller breasts Plunge: low center; works under low-cut tops Push-up: padding for lift/projection Full-coverage: maximum coverage; good for larger sizes Bralette: no underwire; lighter support; lounge wear Strapless: special construction; band must be very supportive Nursing: easy access for breastfeeding; sized larger initially Mastectomy: pocketed for prosthesis; specialty sizing Pregnancy and nursing changes: Significant size changes: Cup: typically up 2-3 sizes by full term Band: up 1-2 sizes due to ribcage expansion Post-baby: cup may decrease, band may stay larger temporarily Nursing bras: Sized at later pregnancy or post-baby Allow milk supply growth (consider 1 cup size larger initially) Easy access for feeding When to re-fit: - Significant weight change (10+ lbs) - Pregnancy - After childbirth and nursing - Hormonal changes - Surgery affecting breasts - Every 1-2 years (gradual changes) - New bra purchase

How to use this calculator

Measure underbust (band): snug around ribcage just below breasts, level all around. In inches.
Measure bust: around fullest part of breasts, wearing thin non-padded bra or bralette. In inches.
Enter both measurements.
Review band size and cup size estimate.
For initial bra: starting point, but try on for actual fit.
For online shopping: cross-reference brand-specific size charts.
For between sizes: try sister sizes for fit alternatives.
For different bra styles (sports, plunge, balconette): try multiple styles in same size to find best fit.
For professional fitting: visit bra-fitting specialist at department store (Nordstrom, Bare Necessities) or specialty boutique.
For pregnancy/nursing: re-measure regularly as size changes significantly.
For post-mastectomy or specialty needs: consult specialty fitters.
For lots of size variation among brands: keep notes on what brand-specific size fits well.

Worked examples

Standard fit calculation

Underbust measurement: 32 inches. Bust measurement: 36 inches. Band size: 32 (already even number) Difference: 36 - 32 = 4 inches → Cup D Initial size: 32D Sister sizes (same volume, different band/cup): 30DD = 32D = 34C = 36B = 38A When shopping: try 32D as starting point. If band too loose, try 30DD. If band too tight, try 34C. Brand variation: same person may wear 32D in some brands, 30DD or 34C in others. Brand-specific fit experience over time helps build vocabulary of "your size in this brand." Recommendation: get professionally fitted at least once to understand your actual fit; then use that as reference for online ordering.

Common over-banded mistake

Woman wears 38C she's comfortable in. But measurement: underbust 32", bust 36". Calculator suggests: 32D Sister sizes: 30DD, 34C, 36B, 38A She's wearing 38C — sister-sized way too far up in band, way too far down in cup. Band probably riding up in back; cup probably gaping; straps probably slipping. Common pattern: women size up in band and down in cup because larger numbers feel "wrong" for cup (D, DD, DDD sounds bigger than B, C). But proper sizing often counterintuitively has larger cup letter with smaller band number. For this woman: try 30D or 32C. Likely much better fit. Professional fitter at department store can guide. This is why bra fitting expertise valuable — what feels "normal" may be very wrong fit.

Pregnancy size progression

Pre-pregnancy: 32B. Underbust 32", bust 34". By 8 weeks pregnant: underbust slightly larger; cup notably fuller. Try 34B. By 20 weeks: underbust 33", bust 38" → 34D. By 36 weeks: underbust 34", bust 40" → 36D. Just before labor: may be 36DD or 38DD. Continued size changes. Post-birth, before nursing established (week 1): bust returns slightly; size still elevated due to engorgement. Established nursing (months 1-12): typically 34-36 band, D-DD cup. Some variation through nursing relationship. Post-weaning (months 1-3): typically returns to pre-pregnancy size or slightly larger. Tissue redistribution permanent for many women. Practical: don't invest in many same-size bras during pregnancy/nursing. Buy minimum sizes needed for current stage; replace as you grow. Maternity/nursing brands: ones that accommodate size growth (extra hooks/closures) helpful.

When to use this calculator

Use this calculator for initial bra fitting guidance, online bra shopping, sister-size finding, sizing through pregnancy/nursing, or learning sizing fundamentals.

Pair with shoe-size, ring-size, and other clothing-size calculators.

Important bra sizing considerations:

1. **Calculator is starting point, not definitive.** Actual fit requires trying on; many bras don't fit despite "correct" calculated size.

2. **Industry research shows 70-80% wear wrong size.** Professional fitting often reveals dramatic mismatches.

3. **Sister sizes provide alternatives.** Same volume, different band/cup combinations. Critical concept.

4. **Brand sizing varies enormously.** Same "34D" fits differently across brands. Keep brand-specific notes.

5. **Breast shape matters beyond size.** Full-on-top vs. full-on-bottom shapes fit different styles better.

6. **Different styles fit differently at same size.** T-shirt vs. plunge vs. balconette all fit differently.

7. **Tight-band approach used by specialty fitters.** Many size 32 underbust measurements actually fit better in 30 band.

8. **Band does the work.** Should be horizontal in back, not riding up. Straps should not bear weight.

9. **Pregnancy/nursing requires re-fitting.** Significant size changes; replace bras as you grow.

10. **Professional fitting transformative for many.** Visit specialty boutique or department store for proper fitting.

11. **Cup volume related to gross dimensions.** Larger band with smaller cup letter = same volume as smaller band with larger cup letter.

12. **Comfort matters most.** All-day wear; proper fit reduces back pain, improves posture, eliminates discomfort.

Common mistakes to avoid

Sizing up in band when cups don't fit. Sister-size up in cup at same volume.
Sizing band based on outdated "+4 method." Modern fitting uses underbust directly or rounds up to even number.
Wearing same size in all brands. Brand variations dramatic; expect to need different sizes across brands.
Ignoring breast shape. Same size in different styles fits differently; shape matters beyond measurement.
Strap-bearing weight. Band does 90% of support work; if straps bearing weight, band too loose.
Not getting professional fitting. Many women find dramatic improvement from properly trained fitter.

Frequently Asked Questions

Sources & further reading

Bra Industry Resources — Lingerie and Bra Industry (general reference)
Women's Health Resources — U.S. Office on Women's Health
Body Measurement Standards — International Organization for Standardization

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