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Bra Size Calculator

Calculate bra size from bust and band measurements. Convert between US, UK, EU, French, and Australian sizing.

Bra Size Worksheet
Size Converter Worksheet

Convert bra sizes between different regional standards.

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How to Find Your Bra Size

Measure your bust and band circumference, then use the calculator above. The difference between bust and band determines your cup size.

Measuring Tips

  • Bust: Measure loosely around the fullest part of the chest while wearing a bra
  • Band: Measure firmly (not tightly) directly under the breasts
  • Stand straight with arms at your sides
  • Keep the tape level all the way around
  • Measure to the nearest 1/4 inch or 1/2 cm

Cup Size Chart (US)

  • AA: Less than 1 inch difference
  • A: 1 inch difference
  • B: 2 inch difference
  • C: 3 inch difference
  • D: 4 inch difference
  • DD/E: 5 inch difference
  • DDD/F: 6 inch difference

Signs of a Poor Fit

  • Band rides up in the back — band is too large, go down a size
  • Straps dig in or fall off — band isn't supporting enough, try a smaller band
  • Cups overflow or gape — wrong cup size or shape for your body
  • Underwire sits on breast tissue — cup is too small or wrong style

Studies suggest 70-85% of women wear incorrectly fitted bras, most commonly a band too large and cup too small.

Understanding Sister Sizes

Sister sizes share the same cup volume but with different band sizes. If your exact size isn't available, sister sizes offer an alternative fit.

  • Up one band, down one cup: 34C → 36B
  • Down one band, up one cup: 34C → 32D
  • Only move 1-2 sister sizes — beyond that, proportions change too much

Cup volume is relative to band size. A 32D and 36B hold the same volume, but the band length and wire width differ significantly.

International Size Conversion

  • US/UK bands: Same numbering (32, 34, 36). Cup letters diverge above D (US DD = UK DD, US DDD = UK E)
  • EU: Uses centimeters (US 32 = EU 70, US 34 = EU 75, US 36 = EU 80)
  • France: EU band + 15 (US 34 = EU 75 = FR 90)
  • Australia: Uses numbered back sizing (AU 10 = US 32, AU 12 = US 34)

Sizing varies between manufacturers even within the same country. Always try before buying when switching brands.

When to Get Remeasured

Measure every 6-12 months, or sooner after weight changes of 5+ lbs, pregnancy, breastfeeding, hormonal changes (menopause, starting/stopping birth control), or whenever your current bra feels uncomfortable.

Bra Types and When to Wear Them

  • T-shirt bra: Molded cups with no visible seams. Best under fitted tops and lightweight fabrics
  • Balconette: Wide-set straps with a horizontal neckline. Works with wide or square necklines
  • Plunge: Deep V neckline between cups. Designed for low-cut tops and dresses
  • Sports bra: Compression or encapsulation design for exercise. Should minimize bounce without restricting breathing
  • Bralette: Unstructured, no underwire. Best for smaller cup sizes or loungewear
  • Strapless: Relies entirely on band support. Band fit is critical — go down a band size for security

Band Lifespan and Care

Most bras last 6-12 months of regular wear before the elastic loses support. The band does 80% of the support work (not the straps), so a worn-out band means the entire bra is ineffective. To extend lifespan: hand wash or use a lingerie bag on the delicate cycle, air dry instead of machine drying, and rotate between at least 3 bras so each gets rest between wears. Hook on the loosest setting when new — as the band stretches over time, tighten to the middle and then innermost hooks.

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Frequently Asked Questions

How do I measure my bra size?

Take two measurements in inches. Wrap the tape firmly, not tight, directly under the breasts for the band, keep it level and round to the nearest even number. Then measure loosely around the fullest part of the bust while wearing a well-fitted bra. Each inch of difference between bust and band is one cup size.

What are sister sizes?

Sister sizes hold the same cup volume on a different band. Going down one band size and up one cup letter keeps the volume, so 34C, 32D and 36B are sister sizes. They help when the cup fits well but the band feels too loose or too tight around the ribcage.

How do US and UK bra sizes differ?

Band numbers are the same in both systems, but cup letters split after D. US sizing runs D, DD, DDD, G, while UK sizing runs D, DD, E, F, FF, G, GG, H. The same letter above D therefore means a different cup in each system, so check which system a label uses.

What is a US 34 band in EU sizes?

A US 34 band is EU 75, and a US 36 band is EU 80. EU bands are measured in centimeters and move in steps of 5 for each 2-inch US step. Cup letters match closely through D, then drift apart at larger sizes, so check a brand size chart for bigger cups.