Bra Size Calculator

How to Measure Your Bra Size at Home

The bra size calculator converts your body measurements into the correct bra size. Studies suggest 80% of women wear the wrong bra size — most commonly too large a band with too small a cup. A properly fitting bra should have 80–90% of breast support coming from the band, with straps providing only gentle supplemental support.

You need two measurements and a soft measuring tape: Band measurement: Around your ribcage directly under your bust, tape parallel to floor. Breathe normally. Round to nearest inch. Bust measurement: Around the fullest part of your chest (typically at nipple level), tape parallel to floor. Don't compress breast tissue. Lean forward 45° for the most accurate measurement. Take both measurements while wearing a non-padded or lightly padded bra.

Bra Measurement: Band Size and Cup Size Formulas

Two common methods exist — use the method that produces the best fit for you:

• Traditional US method: If underbust is even, add 4"; if odd, add 5". Example: 30" underbust → 34 band; 31" underbust → 36 band. Cup = bust − calculated band size.
• Modern snug method (preferred by fitting specialists): Band size = underbust measurement (rounded to nearest even number). Example: 30" underbust → 30 band. Cup = bust − underbust measurement.

Cup size from difference (bust minus band): 0" = AA | 1" = A | 2" = B | 3" = C | 4" = D | 5" = DD (E) | 6" = DDD (F) | 7" = DDDD (G) | 8" = H | 9" = I | 10" = J. Example using snug method: 32" underbust, 37" bust. Band = 32. Cup difference = 37 − 32 = 5" = DD. Size = 32DD.

Bra Size Converter — Sister Sizes

A crucial concept in bra fitting: sister sizes. The volume of the cup stays the same when you go up one band size and down one cup size (or vice versa). This matters when a bra you love doesn't come in your exact size:

• 34C is a sister size to 32D and 36B — same cup volume, different band
• 36DD is a sister size to 34E and 38D
• 32DDD is a sister size to 30DDDD(H) and 34DD

If a bra fits everywhere except the band is too tight: go up one band size, down one cup letter. If band is too loose: go down one band size, up one cup letter. Sister sizing lets you achieve the correct cup volume even when your exact size isn't available.

Signs You're Wearing the Wrong Bra Size

• Band rides up in back: Band is too large. The back should be level with the front underwire. If it rides up, go down a band size (and up a cup size).
• Straps digging in or falling off: If straps dig in painfully, the band isn't doing its job — try a smaller band. If straps slip off, check if the band is too large or try a different strap style.
• Cup spillage ("double bubble"): Breast tissue overflowing the top or sides of the cup means the cup is too small. Go up a cup size.
• Cup gaping or wrinkling: Empty space in the cup means the cup is too large. Go down a cup size.
• Center gore not lying flat: The center gore (between the cups) should lie flat against your sternum. If it pokes out, the cups are too small — go up a cup size.
• Underwire poking or sitting on breast tissue: Underwire should sit in the breast crease entirely on ribcage, not on breast tissue. If it pokes, the band is too large or cup too small.

Bra Size by Country — International Conversion Chart

Bra sizing varies significantly by country. Key conversions for common US sizes:

• US 34B → UK 34B → EU 75B → FR/BE/ES 90B → IT/AU 12B
• US 34D → UK 34D → EU 75D → FR/BE/ES 90D
• US 36DD → UK 36E → EU 80E → FR/BE/ES 95E
• US 32DDD → UK 32F → EU 70F → FR/BE/ES 85F

EU/French band sizing = US band size + 15 (roughly). UK sizing: cups are labeled differently above D — UK uses E, F, FF, G, GG where US uses DD, DDD, DDDD, etc. When shopping internationally or online from European brands, always check the brand's specific size chart as conventions vary.

Bra Fitting Tips for Different Body Types

• Full bust (G+ cup): Look for bras with three or more rows of hooks, wide straps, and full coverage cups. Brands specializing in larger cups: Elomi, Panache, Fantasie, Freya, Curvy Kate.
• Full bust at a small band (28–32 band): Called "small back, large cup" — hard to find in mainstream stores. Specialty retailers like Nordstrom, HerRoom, or dedicated boutiques carry these. Common sizes: 28F, 30G, 32H.
• Post-pregnancy/nursing: Breasts often change 1–2 cup sizes during pregnancy and nursing. Nursing bras should be measured during nursing, in the morning before the first feeding for the largest size you'll need.
• Asymmetrical breasts: Normal — most women have one breast slightly larger. Fit to the larger breast and use a pad or insert in the smaller cup if needed.

Frequently Asked Questions

How do I measure my bra size accurately?

Measure underbust (snugly around ribcage under breasts) and bust (loosely around fullest part, usually at nipple level). Calculate difference: bust − underbust = cup size indicator (1"=A, 2"=B, 3"=C, 4"=D, 5"=DD). For band: use underbust measurement directly (snug method) or add 4" (traditional method). Try both and see which produces a better fit. Remeasure every 6–12 months, or after significant weight changes, pregnancy, or breastfeeding.

What is the most common bra size?

The most commonly sold bra size in the US is 34B or 34C, but this likely reflects what's most widely available rather than what women truly need. Fitting experts estimate that when properly measured, the average size is closer to 34D or 36C — many women are wearing sizes 2–3 cup sizes smaller than they need. The "average" is shifting as awareness of proper bra fitting increases and more extended size ranges become available.

How often should you replace your bra?

With regular wear and proper care: 6–12 months per bra. Signs it's time to replace: band has no more tightening room on the tightest hook (it should start on the loosest and tighten as the band stretches over time), underwires poking through, cups losing shape, or support declining despite proper care. Rotate 3–5 bras to extend lifespan — elastic needs 24 hours to recover between wearings. Hand wash or use a lingerie bag on delicate cycle for longest life.

What does 34C vs 34D mean?

The number (34) is the band size — the circumference around your ribcage in inches. The letter (C, D) is the cup size — the volume of the cup relative to the band. A 34C has a cup 3" larger in circumference than the band; a 34D has a cup 4" larger. Important: a 34D cup is different from a 38D cup — the number changes the actual cup volume (38D has more volume than 34D even though both are "D" cups). This is why sister sizing matters — a 36C and 34D hold the same breast volume.