👙 Bra Size Calculator

About 👙 Bra Size Calculator

Welcome to the Bra Size Calculator, a free online tool that helps you determine your correct bra size from just two measurements: your band (underbust) and bust. Get instant results in 6 international sizing systems (US, UK, EU, French, Italian, and Australian), along with sister size recommendations and personalized fit tips.

How to Measure for a Bra

What You Need

• A soft measuring tape (fabric or flexible plastic, not a rigid metal one)
• A well-fitting, non-padded bra (or measure without a bra for best accuracy)
• A mirror (optional, to check the tape is level)

Step 1: Measure Your Band (Underbust)

Wrap the measuring tape snugly around your ribcage, directly below your breasts. The tape should be level all the way around and firm against your skin without digging in. Breathe normally and note the measurement. This gives you your band size.

Step 2: Measure Your Bust

Wrap the tape around the fullest part of your bust, keeping it parallel to the floor. Do not compress breast tissue; the tape should be snug but not tight. Stand up straight and note this measurement. This gives you your bust measurement.

How Bra Size Is Calculated

Band Size

The underbust measurement is rounded to the nearest even number to determine the US/UK band size. For example, if your underbust measures 31.5 inches, your band size is 32. EU, French, Italian, and Australian band sizes are then derived from the US band using standard conversion tables.

Cup Size

The cup size is determined by the difference between the bust and underbust measurements. Each inch of difference corresponds to a cup letter:

• 0 inches: AA
• 1 inch: A
• 2 inches: B
• 3 inches: C
• 4 inches: D
• 5 inches: DD/E (US) or DD (UK)
• 6 inches: DDD/F (US) or E (UK)
• 7+ inches: Size continues to increase with each additional inch

Understanding International Sizing

US Sizing

US bra sizes use even numbers for bands (30, 32, 34, etc.) and letter cups that double D (DD, DDD, DDDD) before switching to alphabetical letters. This system is standard in the United States and Canada.

UK Sizing

UK sizes use the same band numbering as the US but have a different cup progression after D: DD, E, F, FF, G, GG, H, HH, J, JJ. Many premium lingerie brands use UK sizing.

EU Sizing

EU (European) sizes use centimeter-based bands (65, 70, 75, 80, etc.) and a simpler alphabetical cup sequence (A, B, C, D, E, F, G, H...). This system is used across most of Continental Europe.

French and Italian Sizing

French (FR) sizes add 15 cm to the EU band (EU 70 = FR 85). Italian (IT) sizes use a numbering system (1, 2, 3, 4...) for bands. Both use the same cup letters as EU sizing.

Australian Sizing

Australian (AU) sizes use even numbers starting from 6 for bands (6, 8, 10, 12...) and follow the UK cup progression. This system is also used in New Zealand.

What Are Sister Sizes?

Sister sizes are bra sizes that share the same cup volume but differ in band length. For each band size you go up, you go down one cup letter, and vice versa. For example, these are all sister sizes with the same cup volume:

• 30D = 32C = 34B = 36A
• 32DD = 34D = 36C
• 36D = 38C = 34DD

Sister sizes are useful when your exact size is unavailable, when a particular brand runs tight or loose, or when you prefer a different band fit.

Signs of a Good Fit

• The band sits level around your body and feels snug on the loosest hook (so you can tighten it as the elastic ages).
• The center gore (the fabric between the cups) lies flat against your sternum.
• The underwire (if present) follows the natural crease under each breast without poking or sitting on breast tissue.
• The cups contain all breast tissue without gapping, wrinkling, or spillover.
• The straps stay in place without digging into your shoulders. You should be able to fit two fingers underneath them.

Common Fit Problems and Solutions

Band Rides Up in the Back

If the band rides up, it is too loose. Try going down a band size (and up a cup size to maintain the same cup volume). The band provides 80% of a bra's support, so a snug fit is essential.

Cups Overflow or Bulge

If breast tissue spills out of the cups (sometimes called "quad-boob"), the cups are too small. Go up one or two cup sizes while keeping the same band size.

Cups Wrinkle or Gap

If there is empty space in the cups, they are too large. Try going down a cup size. If the issue is only at the top, try a different cup shape (like a balconette).

Straps Dig In or Fall Off

Digging straps often mean the band is too large and the straps are compensating for the lack of support. Falling straps may indicate you need a style with narrower-set or convertible straps.

Tips for Accurate Measurement

• Measure in front of a mirror to ensure the tape is level all the way around.
• Measure while wearing a non-padded bra for the most accurate bust measurement, or measure without a bra entirely.
• Do not hold your breath — breathe normally while taking measurements.
• Measure at least twice and take the average for best accuracy.
• Do not add inches to your underbust measurement. Many older fitting guides add 4-5 inches, but modern sizing does not require this.

Frequently Asked Questions

How do I measure my bra size at home?

To measure your bra size at home, you need a soft measuring tape. First, measure your underbust (band) by wrapping the tape snugly around your ribcage directly under your breasts. Then measure your bust at the fullest point of your chest, keeping the tape parallel to the ground. Enter both measurements into the calculator to get your size in multiple international systems.

What are sister sizes in bras?

Sister sizes are bra sizes with equivalent cup volumes but different band sizes. For example, 34C, 32D, and 36B are all sister sizes because they share the same cup volume. If your usual size does not fit perfectly, trying a sister size can help you find a more comfortable fit, especially when switching between brands.

How do US bra sizes compare to European sizes?

US and EU bra sizes differ in both band and cup notation. US band sizes are in inches (32, 34, 36) while EU uses centimeters (70, 75, 80). Cup letter progression also differs: US uses AA, A, B, C, D, DD, DDD while EU uses AA, A, B, C, D, E, F. This calculator automatically converts between US, UK, EU, French, Italian, and Australian sizing systems.

How often should I remeasure my bra size?

You should remeasure your bra size every 6 to 12 months, or whenever you experience weight changes, pregnancy, hormonal changes, or notice your current bras no longer fit well. Body measurements can change significantly over time due to various factors, and wearing the wrong bra size can cause discomfort and poor support.

Why do bra sizes vary between brands?

Bra sizes vary between brands because there is no universal manufacturing standard. Each brand uses slightly different patterns, materials, and fit models. A 34C from one brand may fit differently from another. This calculator gives you a starting point, but always try bras on and consider the specific brand's size chart for the best fit.

Should I add 4 inches to my underbust measurement?

No. The "plus 4" method is outdated. It originated when bras were made from non-stretch materials and needed extra room. Modern bras use elastic bands, so your band size should be close to your actual underbust measurement (rounded to the nearest even number). This calculator uses the modern method for the most accurate results.

What if my measurements fall between sizes?

If your measurements fall between sizes, try both the larger and smaller options. Most people find one more comfortable than the other. You can also try sister sizes: if the band is right but the cup is not, adjust the cup; if the cup volume is right but the band is not, try the sister size.

Additional Resources

• Brassiere Measurement - Wikipedia
• Bra Size - Wikipedia