Bra Size Converter
How it works: Enter your current bra size to convert across regions, or provide your underbust and bust measurements to estimate a size. We align your measurements to standard band ladders (US/UK in inches, EU/JP in 5cm steps) and map cup sizes from the bust-underbust difference. Sister sizes show alternate band-cup combinations with the same volume. All calculations run locally in your browser.
Overview
Quickly convert bra sizes between US/UK, EU, FR/ES, AU/NZ, and JP, or estimate a size from your bust and underbust measurements. This bra size converter normalizes band numbers and cup letters — including UK double letters — then displays equivalents across regions. If you're starting from measurements, pick inches or centimeters, choose a rounding rule, and we'll map your cup size from the bust-underbust difference and recommend a band size. You'll also see two sister sizes for alternate fits. All calculations run locally in your browser. Brands vary, so treat results as a starting point and check each label's fit guide.
About
About Bra Size Converter
International bra sizing blends band measurements with cup steps that aren't standardized across every brand. This converter uses a practical, widely used mapping: US/UK bands in inches, EU/JP in 5-cm steps, FR/ES as EU+15, and AU/NZ aligned to UK via a well-known ladder (e.g., UK 34 ↔ AU 12). Cups increase roughly one step per 1″ (≈2.5 cm) of bust-underbust difference. UK sizing often uses double letters (DD, FF, GG), while EU/JP prefer single letters. To keep things consistent, we convert cups to an internal index, then render them in your preferred style. Because brands, materials, and shapes differ, treat results as estimates and try adjacent sister sizes to dial in comfort.
Features:
- Convert between US/UK, EU, FR/ES, AU/NZ, and JP sizing systems
- Estimate size from underbust and bust measurements
- Support for UK double letters (DD, FF, GG) and single-letter cups
- Calculate sister sizes for alternate fits
- Modern or traditional (+4) band rounding rules
- Copy any size to clipboard with one click
- 100% client-side calculation for complete privacy
FAQ
What are sister sizes?
Sister sizes are bra sizes with the same cup volume but different band-cup combinations. For example, 34C, 32D, and 36B are sister sizes. Going up one band size and down one cup size (or vice versa) maintains the same cup volume while adjusting the band fit.
Why doesn't my usual brand match exactly?
Bra sizing varies significantly between manufacturers due to differences in materials, construction, and regional standards. Use our converter's results as a starting point, then check each brand's specific size chart and consider trying sister sizes for the best fit.
Do you use the +4 rule?
We default to a modern nearest-band approach, which many experts now recommend. However, you can toggle to the traditional +4 method (adding 4-5 inches to your underbust measurement) if you prefer that sizing convention.
Are UK and US cup sizes identical?
UK and US sizing are generally similar, but the UK commonly uses double letters (DD, FF, GG, HH) where US sizing might use single letters or different naming (like DDD instead of E). Our converter handles both styles and lets you toggle between them.
How do I measure for the calculator?
For underbust: Measure snugly around your ribcage directly under your bust. For bust: Measure around the fullest part of your bust while standing. Keep the tape parallel to the ground and don't pull too tight. Measurements should be taken while wearing an unpadded bra or no bra.
Is this medical advice?
No. This tool provides informational estimates only and is not a substitute for professional fitting or medical advice. For the most accurate fit, consider getting professionally fitted at a lingerie store.
What if my measurements fall between sizes?
If you're between sizes, try both and see which feels more comfortable. Also check the sister sizes we provide — they have the same cup volume but different band fits, which might work better for your body shape.
Why do some regions skip certain cup letters?
Different regions have different naming conventions. For example, US/UK sizing traditionally uses DD instead of E, and may use DDD or F interchangeably. EU and JP sizing typically use single letters without doubles. Our converter normalizes these differences.