Bra Size Calculator – Find Your Perfect Fit

How to Measure for Bra Size: Band and Cup

Bra size has two components: band size (the number) and cup size (the letter). Both require accurate measurements taken with a flexible measuring tape. Wearing a non-padded bra or no bra during measurement ensures the most accurate results. Stand in front of a mirror to confirm the tape is level all the way around your body.

Step 1: Band measurement (underbust)

• Measure snugly around your ribcage directly under the bust, in inches
• Keep the tape level and pull it firm but not tight — you should be able to slide one finger underneath
• Round to the nearest even number. If the measurement is odd, round up to the next even number
• Example: 30.5" → round up to 32 → Band size 32

Step 2: Bust measurement (overbust)

• Measure loosely around the fullest part of your chest, keeping the tape horizontal
• Do not compress the tissue — let the tape rest gently
• Round to the nearest whole number
• For best accuracy, lean forward at a 90-degree angle and measure — this captures fuller bust shapes more accurately

Step 3: Calculate cup size

• Cup difference = Bust measurement − Band size
• 0" = AA, 1" = A, 2" = B, 3" = C, 4" = D, 5" = DD/E, 6" = DDD/F, 7" = G

Example: Underbust 30" → Band 32. Bust 34" → Difference = 34 − 32 = 2" → Cup B → Size 32B.

Many professional bra fitters recommend taking measurements at three different times during the day, since your body shape can shift slightly due to fluid retention, posture, and physical activity. Taking an average of these three measurements produces the most reliable starting size.

Understanding Band Size and Cup Volume

The band size is the foundation of bra fit. It provides roughly 80% of the support, while the straps contribute only about 20%. A properly fitting band should sit parallel to the floor around your torso, feel snug on the loosest hook (so you can tighten it as the elastic wears), and not ride up in the back.

Cup volume is relative to band size — a D cup on a 32 band is significantly smaller in volume than a D cup on a 38 band. This is why a 32D person looks very different from a 38D person. The letter alone does not convey absolute breast size; it represents the proportional difference between the ribcage and the bust.

These approximate volumes illustrate why cup size without band size is meaningless. When shopping, always consider both measurements together.

Sister Sizes: Finding Equivalent Fits

Sister sizes share the same cup volume but differ in band length. If your size is unavailable, a sister size offers an equivalent cup volume with a tighter or looser band. This concept is essential when a brand's sizing runs large or small, or when your exact size is out of stock.

Going up in band size = same cup volume, but the band will be looser. Going down in band size = same cup volume, but the band will be tighter. Adjust the cup letter accordingly (one letter up when going down in band, one letter down when going up in band). Sister sizing is particularly useful for online shopping, where you may need to adjust between brands.

International Bra Size Conversion

Bra sizing systems differ significantly between countries. Brands manufactured in Europe, Asia, or Australia use their own sizing standards. Here is a conversion chart for the most common standards:

EU band sizes use centimeters: US 32 = EU 70, US 34 = EU 75, and so on (add approximately 38 to the US band to get the EU equivalent). Cup letters diverge above a D cup: US DD = UK E = EU E. Always consult the specific brand's size chart, as measurements can vary even within the same country's system.

Bra Types and When to Wear Them

Different bra styles serve different purposes. Choosing the right style for your outfit and activity level ensures both comfort and proper support throughout the day.

For maximum comfort, rotate between at least three bras to allow the elastic to recover between wears. Hand-washing and air-drying extends the lifespan of bras significantly — machine washing and drying can break down elastic fibers and warp underwires within a few months.

Signs Your Bra Doesn't Fit Correctly

Studies suggest that approximately 80% of women wear the wrong bra size. Here are the most common fit issues and what they indicate:

• Band rides up in the back: The band is too loose. Try a smaller band size (e.g., move from 36 to 34) and go up one cup letter to maintain volume.
• Straps dig into shoulders: The band is not providing enough support, forcing the straps to bear the weight. Tighten or size down in the band.
• Cup spillage (quad-boob): The cup is too small. Go up one or two cup sizes while keeping the same band.
• Gapping at the top of the cup: The cup is too large, or the bra style doesn't suit your breast shape. Try a smaller cup or a different cut (e.g., plunge instead of full-coverage).
• Center gore doesn't lie flat: The cups are too small. The center gore (the piece between the cups) should rest flat against the sternum. If it floats away from your chest, increase the cup size.
• Underwire pokes or sits on breast tissue: The cup is too small, or the wire shape doesn't match your breast root. The wire should encircle the breast tissue completely and rest on the ribcage.
• Band feels tight on the tightest hook immediately: The band is too small. Start on the loosest hook so you can tighten as the bra stretches over time.

A professional bra fitting at a specialty lingerie store can help identify these fit issues. Many stores offer free fittings and carry a wider range of sizes than department stores or online-only retailers.

How Bra Size Changes Over Time

Bra size is not a fixed measurement — it changes throughout a woman's life due to a variety of biological and lifestyle factors:

• Puberty: Breast development typically begins between ages 8 and 13 and continues for 3–5 years. First bras are usually training bras or soft bralettes in sizes A–B.
• Weight changes: Breasts contain fatty tissue. Gaining or losing 10+ pounds often changes both band and cup size. Weight gain typically increases both measurements; weight loss may reduce cup size more than band size.
• Pregnancy and breastfeeding: Most women go up 1–3 cup sizes during pregnancy and breastfeeding. A nursing bra with flexible sizing accommodates the rapid changes that occur during this period.
• Menstrual cycle: Hormonal fluctuations can cause breasts to swell by up to a half cup size in the week before menstruation. Some women keep two sets of bras for different phases of their cycle.
• Menopause: Hormonal shifts during menopause change breast density and composition, often resulting in a softer, less dense breast that may need a different cup shape for proper support.
• Exercise and muscle changes: Chest exercises (bench press, push-ups) can change the measurements under the bust, potentially affecting band size. Significant weight training may require re-measurement.

Re-measuring every 12–18 months, or after any major body change, ensures you always wear the correct size. Wearing an ill-fitting bra over long periods can contribute to back pain, poor posture, and skin irritation.

Bra Care and Longevity Tips

A well-made bra should last 6–12 months with regular wear and proper care. Extending bra life saves money and keeps the fit consistent. Follow these guidelines for maximum longevity:

• Hand-wash when possible: Use cool water and mild detergent. Swirl gently for 2–3 minutes, rinse thoroughly, and press water out without wringing.
• Machine washing: If you must machine-wash, use a lingerie bag, hook the bra closed to prevent snagging, and select the delicate cycle with cold water.
• Never use a dryer: Heat degrades elastic fibers and warps molded cups. Lay bras flat or hang by the center gore to air-dry.
• Rotate your bras: Give each bra 24–48 hours to rest between wears so the elastic recovers its shape. Owning 3–5 everyday bras makes rotation easy.
• Store properly: Stack molded bras in a drawer with cups nested inside each other. Avoid folding one cup into another, which can crease and deform the padding.

Signs that a bra needs replacing include: elastic that no longer springs back when stretched, a band that feels loose even on the tightest hook, cups that have lost their shape, or visible pilling and fabric thinning.

International Bra Size Chart

Bra size equivalents across US/UK, EU, FR, and AU systems. Sizing varies by brand, so use this chart as a starting point and always check the manufacturer's specific size guide.