Bra Size Calculator

How to measure bra size and how to calculate bra size

This bra size calculator and bra size converter determines your band and cup size across US/CA, UK, EU (EN 13402), French/Belgian/Spanish (FR/BE/ES), and Australian/New Zealand sizing standards. You can enter your bust and underbust measurements in either inches or centimeters, or switch to the converter tab to translate an existing bra size between countries.

1. Measure your band size (underbust): Stand straight and wrap a flexible measuring tape snugly and horizontally around your ribcage directly underneath your breasts. Round to the nearest ¼ inch or 0.5 cm. For US and UK sizing, the calculator rounds your underbust measurement in inches to the nearest even whole number (`Math.round(underbust / 2) × 2`). For EU (EN 13402) sizing, it rounds your underbust in centimeters to the nearest 5 cm step and subtracts 10 cm (`Math.round(underbustCm / 5) × 5 − 10`), and adds 15 cm to the EU band for FR/BE/ES sizing.
2. Measure your bust size (overbust): While wearing an unpadded, well-fitted bra and keeping your arms relaxed at your sides, wrap the tape loosely and level across the fullest part of your breasts without compressing breast tissue.
3. Calculate the cup size from the difference: Subtract your underbust measurement from your bust measurement. In US, UK, and Australian sizing, the calculator takes the whole-inch difference (`Math.floor(bustInches − bandInches)`), stepping up one cup letter per inch starting at AA for less than 1 inch, A for 1 inch, B for 2 inches, C for 3 inches, and D for 4 inches. In Continental European (EU and FR/BE/ES) sizing, the calculator takes `Math.floor((bustCm − bandCm) / 2)`, where each 2 cm difference between bust and raw underbust steps up one cup letter (equivalent to a 10–11 cm difference over the labeled EU band for AA, 12–13 cm for A, and so on).

International bra size chart (US, UK, EU, FR, and AU/NZ)

Band and cup labels vary significantly by region. Use the reference tables below to compare international band sizes and cup progressions:

What the result includes

• Estimated bra size across 7 sizing conventions: US/CA, UK (including UK dress code), EU (EN 13402), FR/BE/ES, Australia/New Zealand, and legacy Underbust +4 sizes.
• Bust-to-band difference in both inches and centimeters, plus US sister sizes (one band size down with one cup size up, and one band size up with one cup size down).
• International bra size converter tab to convert any known band and cup combination between US/CA, UK, EU, FR/BE/ES, and AU/NZ systems.

Important caveats

Bra sizing is not legally standardized across clothing brands, and fabric elasticity, cup cut, and underwire shape vary from one manufacturer to another. Treat calculated sizes as a starting point: if the band rides up your back, try one band size down and one cup size up; if the cups gape or overflow, adjust the cup letter while keeping the band snug.

Frequently asked questions

What is my bra size, and how to measure bra size accurately at home?

To find out what your bra size is at home, take two measurements with a soft tape measure while wearing a non-padded bra: your snug band (underbust) measurement directly beneath your breasts, and your loose bust (overbust) measurement across the fullest part of your chest. Enter both numbers above to see how to calculate bra size in US, UK, EU, French, and Australian standards.

How does a UK to US bra size converter work for D+ cups?

US and UK band numbers (28, 30, 32, 34, 36, and up) are identical, and cup letters match from AA through DD. Above DD, the two systems diverge: UK sizing uses double letters (DD, E, F, FF, G, GG, H, HH), whereas most US brands progress through single letters or multi-D labels (DD/E, DDD/F, DDDD/G, H, I, J). For example, a UK 34FF corresponds to a US 34H.

How do sister sizes work in a sister size bra calculator?

Cup volume scales with band length—a 34C cup holds more volume than a 32C cup. Sister sizes are bra sizes that hold approximately the same cup volume on a different band: to find your sister size with a tighter band, go down one band size (2 inches) and up one cup letter (for example, 34C → 32D). For a looser band, go up one band size and down one cup letter (for example, 34C → 36B).

What is the difference between modern bra sizing and the Underbust +4 method?

Modern elastic bra bands are engineered to stretch to your actual underbust measurement in inches (so a 32-inch ribcage wears a 32 band). The legacy “Underbust +4” method dates back to non-stretch fabrics and adds 4 inches to the underbust before calculating cup size, resulting in a looser band and a smaller cup letter (for example, 36D instead of 32D). Very few contemporary brands still use +4 sizing.