Bra Size Calculator

What this calculator does

The Bra Size Calculator estimates a bra size from two measurements: the bust circumference and the underbust circumference. It returns a US/Canada size, a UK size, European sizes under EN 13402, French and Belgian sizes, and an Australian/New Zealand dress-code equivalent. It also shows the underbust-plus-four variants that some manufacturers still use.

Bra sizing is not fully standardized. Two brands can label the same measurements differently, and cup volume for a given letter varies between manufacturers. Treat the result as a starting point for trying on bras, not as a guaranteed fit.

How to use this calculator

1. Measure the underbust snugly around the ribcage, directly beneath the breasts.
2. Measure the bust around the fullest part of the chest while standing straight.
3. Choose inches or centimeters and enter both measurements.
4. Click Calculate and compare the sizes shown for each region.

For the default example, a 38-inch bust and a 34-inch underbust produce a US/Canada 34D. The same measurements convert to 75E in the EU standard, 90E in French sizing, and dress code 12D in Australia/New Zealand.

Bra size formulas

Difference = bust − underbust
US band   = underbust rounded to the nearest even inch
US cup    = AA, A, B, C, D, DD/E, DDD/F, and so on
EU band   = 60 + (US band − 28) × 2.5 cm
FR band   = EU band + 15 cm

The cup letter comes from the difference in inches. A difference below 1 inch is AA, 1 inch is A, 2 inches is B, 3 inches is C, 4 inches is D, and each additional inch advances the cup letter. The EU cup in this calculator is estimated from the bust circumference minus the EU band size in centimeters. The underbust-plus-four method adds four inches to the band while keeping the same cup letter.

What the results mean

The US/Canada row is the primary estimate. The UK row uses UK cup letters, which differ from US letters at larger cup sizes. The EU and French rows use centimeter band sizes. The Australia/New Zealand row uses the local dress-code convention rather than a band number.

A sister size is a nearby size with a different band and cup combination that holds a similar volume. If the calculated band feels too tight, a larger band with a smaller cup may fit; if it feels too loose, the reverse may help.

Assumptions and limitations

• Measurements should be taken without a padded bra and with the tape level and snug, not tight.
• The calculator uses a nearest-even band and a simple inch-difference cup scale. It does not account for breast shape, projection, root width, or style.
• The underbust-plus-four method is shown for compatibility, but most modern US and UK brands use the measured underbust.
• Regional conversions are approximate. EU and French cup letters are not identical to US letters.
• This is a fitting estimate, not medical advice. A professional fitting is the most reliable option.

Frequently asked questions

How should I measure my underbust?

Wrap a soft tape around the ribcage directly under the breasts, keeping it level and snug. Breathe normally and do not pull the tape tight. Round the result to the nearest whole measurement before entering it.

Why is my calculated size different from the bra I usually wear?

Brand sizing, fabric stretch, cup shape, and style all affect fit. A 34D from one brand may fit like a 32DD or 36C from another. Use the result as a starting point and try nearby sizes.

What is the underbust-plus-four method?

It is an older sizing convention that adds four or five inches to the underbust to get the band size. Some manufacturers still publish sizes this way. The calculator shows both the measured-band and plus-four results so you can compare.

Reference tables

International band sizes

Cup size by bust-band difference

Location size examples

Conversions are approximate. Fit varies by brand, style, and measurement method.

Source

Reference: Calculator.net — Bra Size Calculator.

Disclaimer

This calculator provides an estimate only and is not medical advice. Bra sizing varies by brand and style. Consult a professional fitter if you have pain, discomfort, or concerns about breast health.