Bra Size Calculator
Calculate your bra size accurately and convert sizes across international standards.
Disclaimer
Look, no calculator can account for the fact that a 34C from one brand fits nothing like a 34C from another. This tool gives you a number to start with, not a number to live by. Try the size it gives you and adjust from there. If your bra is causing you real pain or discomfort on a regular basis, that is worth talking to a doctor or a certified fit specialist about.
Expert Review
This calculator uses standard underbust and overbust measurement methods aligned with US sizing conventions. Cup size is calculated from the difference between bust and band measurements. Results are starting estimates only. Fit can vary a lot by brand, style, and fabric.
Sources
- ThirdLove Bra Fit Guide — band, cup, and sister size methodology
- Lane Bryant Cacique Bra Fit Guide — measurement and fitting instructions
- Wacoal America Bra Fit Calculator — underbust and overbust measurement standards
- Vogue — How to Measure Bra Size for a Proper Fit, 2024
- Olivia Paisley Bra Size Research — 2024 cup volume variation study findings
What Is a Bra Size Calculator?
Bra sizing is genuinely confusing, and many women wear the wrong size without realizing it. This calculator takes two quick measurements you can do at home and figures out your band size and cup size for you. No fitting room and no awkward tape measure moments with a stranger. Just your numbers, your size, and something that actually makes sense.
Benefits
- Gives you a starting size based on your actual measurements, not guesswork
- Works from home without needing a fitting appointment
- Shows sister sizes so you have options when your exact size is not available
- Helps you understand why your current bra may feel uncomfortable or wrong
- Saves time and money by giving you a real size to work from before you shop
- Converts your size to US, UK, and EU sizing for international shopping
Did You Know?
Many women wear the wrong bra size, often because band and cup sizing are genuinely confusing. A band that is too loose and cups that are too small can make both support and comfort much worse.
How Does It Work?
Grab a soft measuring tape. Wrap it around your ribcage, right under your bust, and write that number down. Then measure around the fullest part of your bust. Type both into the calculator. It finds the difference between the two numbers, and that difference is what determines your cup size. One inch difference is an A cup, two inches is a B, and so on. Band size comes from that first measurement. Thirty seconds and you are done.
| Myth | Facts |
|---|---|
| Cup size is a fixed measurement that means the same thing on every bra. | Cup volume changes with band size. A 34D and a 36C hold roughly the same cup volume. |
| If a bra fits in the store, it will always fit. | Bras stretch over time. A bra that fits perfectly today may feel loose in a few months, which is why starting on the loosest hook matters. |
| A tight band means the bra fits too small. | The band is your main support. It should feel snug, not the straps. |
| Bra sizes are standardized across all brands. | Sizing varies widely by brand and country. Always check your measurements against brand sizing charts. |
Privacy Note
This calculator runs entirely in your browser. No measurements, body data, or personal details are stored or shared anywhere. Everything you enter stays on your screen only and is never collected by anyone.
Common Signs Your Bra Is the Wrong Size
The size on the tag means little if the bra is not sitting right. Here are the signs to watch for:
- The band rides up your back instead of sitting level
- Your straps dig into your shoulders or fall off constantly
- The underwire pokes into your breast tissue or sits on it instead of under it
- Cups gap at the top, or your breast spills over the sides
- You have red marks on your skin after taking it off
- The center panel between the cups does not lie flat against your chest
If more than one of these sounds familiar, the size you are wearing is likely not the right fit for you.
Why Your Bra Size Changes and Nobody Tells You
Most women find a size that works and stick with it for years. The problem is your body does not stay the same. Weight changes, hormone shifts, pregnancy, breastfeeding, and even aging all change how you measure. Breasts can also change throughout the month depending on your cycle. It is a good idea to remeasure after major body changes or whenever your current bra stops feeling right.
Your Size Is Sold Out — Here Is What to Try Instead
Your exact size is sold out, and everything in that size looks wrong on you. Sister sizes fix that. A 34D, a 32DD, and a 36C all hold roughly the same cup volume, as an approximate example. They are different sizes on paper, but the cup space is essentially the same. Go up a band size and down a cup letter, or down a band size and up a cup letter, and you will land in the same volume with a different fit around your ribcage.
The Real Reason Your Bra Straps Keep Falling Off
Falling straps feel like a strap problem, but they almost never are. The real issue is usually your band. When the band is too loose, it cannot anchor the straps properly, and they slide off your shoulders no matter how many times you tighten them. Before you adjust your straps again, check your band. If you can pull the band several inches away from your back, it is likely too loose.
When Should You Use This Calculator?
- When your current bra leaves marks, digs in, or rides up your back
- Before buying a new bra online, where you cannot try it on first
- After pregnancy, weight change, or any other body change
- When shopping from a brand you have never bought from before
- If your straps keep slipping or your band keeps moving around
- Anytime you want to double-check that you are still wearing the right size
You deserve a bra that actually fits. Run your measurements through the calculator now and find your real starting size. Two measurements, thirty seconds, and a much better idea of where to begin.