Bra Size Calculator — Find Your Perfect Fit.
Enter your bust and underbust measurements to get your recommended starting size, sister sizes, and international equivalents.
US / CA Sizing System
Your Sister Sizes
Sister sizes have similar cup volume but different band measurements.
If the band feels loose, try a smaller band size.
Starting point based on your measurements.
If the band feels tight, try a larger band size.
International Size Equivalents
| Location | Band | Cup |
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* Your recommended size is based on the measurements you entered and is intended as a starting point. Fit can vary between brands, fabrics, and cup styles.
Bra Size Converter Chart — US, UK, EU & International Sizes
Bra sizing systems vary by country. Use this chart to compare common size labels across verified regions.
Band Conversion MatrixUS / UK / EU / FR / AU / JP
| US / CA | UK | EU | FR / BE / ES | AU / NZ | JP |
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Cup Size MatrixUS / UK / EU / AU / JP
| US / CA | UK | EU | AU / NZ | JP |
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* Bra sizing conventions vary between brands and regions. These conversions are intended as a general sizing reference.
How to Measure Your Bra Size
Finding your exact size requires just two simple measurements. Use a soft measuring tape and measure while wearing a non-padded bra.
Step 1: Underbust
Wrap the measuring tape snugly right under your bust. Ensure it is parallel to the ground all the way around your ribcage.
Step 2: Overbust
Measure loosely around the fullest part of your bust. The tape should rest lightly without pressing into your skin.
Ready with your numbers?
Use our tools to calculate your baseline or compare international sizes.
Why Proper Fit Matters
Wearing a bra that fits correctly provides reliable daily support and all-day comfort. A well-fitted band takes the weight off your shoulders, prevents slipping or digging straps, and ensures your garments sit smoothly against your body.
Because body measurements and bra sizing matrices vary across different manufacturers, learning how to measure your bra size accurately is the most dependable way to establish your baseline. If your current bra feels uncomfortable, browse our bra fit diagnostic guide for common solutions.
Fit Diagnostic & Solutions
A calculated size is a starting point. Your bra should fit comfortably without digging or slipping. Diagnose common fit issues below.
The band is riding up my back
If the band rides up, it is too loose. The band should sit level around your ribcage. Fix: Try a tighter sister size (e.g., if you wear 36C, try 34D).
My straps keep falling off
This often happens when the band is too loose, causing the straps to sit too far apart on your shoulders. Fix: First, tighten the straps. If that fails, go down a band size and up a cup size.
My breasts are bulging out (spillage)
If there is spillage at the top or sides, the cup is too small. Fix: Keep your band size the same, but increase the cup size (e.g., 34B to 34C).
There are gaps in the cups
If there is space between your breast and the cup, the cup is too large or the style doesn't suit your breast shape. Fix: Try going down a cup size (e.g., 34D to 34C).
Still unsure about your size?
Re-check your tape measurements or calculate your starting baseline.
Frequently Asked Questions
Everything you need to know about measuring, bra sizing, and finding your most comfortable fit.
How do I measure my bra size accurately at home?
Take two measurements using a soft tape measure: your band size (snugly under the bust) and your bust size (loosely over the fullest part). Enter these into our calculator for an instant recommended size.
How does the bra size calculator determine my size?
Our calculator compares your bust and band measurements against modern international sizing standards (US, UK, EU, AU) to provide your baseline size and exact sister sizes.
What are sister sizes and how do I use them?
Sister sizes are bras with the same cup volume but different band sizes (e.g., 34C and 32D). If a band feels too loose or tight, stepping up or down to a sister size maintains your cup fit.
Should I measure bra size in inches or cm?
You can use either! Our calculator supports both inches and centimeters, as well as US/CA, UK, EU, and AU international sizing standards.
How often should I re-measure my bra size?
We recommend measuring every 6 months, or whenever you experience weight fluctuations, hormonal shifts, pregnancy, or changes in exercise routines.
Where can I find the full international bra size conversion chart?
We provide a complete, interactive bra size chart on our Size Chart page comparing US, UK, EU, and AU sizing bands and cups.
The Ultimate Guide to Finding Your Perfect Fit
Welcome to BraSizeChecker. Whether you are experiencing discomfort with your current garments or simply want to refresh your wardrobe, knowing your correct measurements is the first step. For decades, individuals have struggled with complex sizing charts, but our bra size calculator simplifies the entire process. By entering just two simple measurements, you can immediately discover your ideal fit across multiple international standards.
How to Measure Bra Size Basics
Determining your size requires precision. Start with a soft measuring tape. First, take your band measurement snugly directly under your bust. Next, take your bust measurement loosely around the fullest part of your chest. For detailed placement diagrams and visual instructions, explore our step-by-step How to Measure Guide. You can calculate in inches or centimeters—whichever unit system you prefer.
Accurate Sizing & Modern Methodology
Unlike outdated fitting charts that arbitrarily add four or five inches to your underbust measurement, we use modern direct underbust fitting standards. Read our transparent Methodology Page to see how our algorithms calculate band numbers, cup letters, and sister sizes. Whether you are shopping for domestic brands or converting sizes across regions, inspect our comprehensive Bra Size Chart and interactive Bra Size Converter.
International Standards: UK & EU Guides
If you are purchasing British or European lingerie, size labels can be confusing. UK brands (like Panache or Freya) use double-letter cup progressions (`DD`, `FF`, `GG`, `HH`). Learn more in our dedicated UK Bra Size Guide. Similarly, European brands follow the metric EN 13402 standard, which you can explore in our EU Bra Size Guide.
Brand Variations & Sister Sizes
It is a well-known secret in the lingerie industry that sizes vary between brands due to fabric elasticity and wire curvature. Our tool gives you an objective baseline. From there, if a band feels too tight or loose in a specific brand, utilize our dedicated Sister Size Calculator to adjust band tightness while maintaining your exact cup volume. If you are experiencing band riding up or cup gaping, visit our Fit Guide Diagnostic Hub.
Stop guessing and start wearing garments that actually support you. Grab your measuring tape and calculate your perfect fit today!