Bra Size Calculator
Estimate your bra size using your underbust and bust measurements. This calculator provides a practical starting size based on common sizing methods for US, UK, and EU systems, then visualizes your measurements with a comparison chart to make the result easier to understand.
Measurement Visualization
After calculation, the chart compares your underbust, bust, and cup difference so you can quickly see how the recommendation is derived.
Your result will appear here
Enter your measurements, select your preferred size system, and click the calculate button.
How a bra size calculator works
A bra size calculator estimates two parts of a bra size: the band size and the cup size. The band size is based primarily on the underbust measurement, while the cup size is estimated from the difference between the bust and underbust measurements. Although the final fit always depends on body shape, breast distribution, brand construction, fabric stretch, and style, a calculator gives a strong starting point that can save time when shopping online or narrowing options in-store.
The basic principle is simple. First, measure the ribcage directly under the bust. This underbust value helps determine the band. Next, measure around the fullest part of the bust. The difference between the full bust and underbust helps determine cup volume. For example, a larger difference generally indicates a larger cup letter. This page uses a common, practical method for translating that difference into cup sizes across US, UK, and EU labeling systems.
It is important to understand that bra sizing is not fully standardized across the entire apparel industry. Different manufacturers may fit tighter or looser, some use more forgiving elastic, and some styles such as balconette, plunge, t-shirt, minimizer, or sports bras may fit differently even within the same brand. That is why many lingerie fit specialists treat calculated size as a starting recommendation rather than a guaranteed final answer.
Why measuring correctly matters
One of the biggest reasons people wear the wrong bra size is inconsistent measuring technique. If the tape is too loose around the ribcage, the recommended band may end up too large, which can reduce support and cause straps to carry too much weight. If the bust measurement is taken over a padded bra or with the tape angled incorrectly, the cup estimate can be inaccurate. Even a one inch difference can change the suggested cup letter in many sizing systems.
A well-fitting bra should provide support from the band first, not from the straps. The center gore should generally sit close to the chest for many styles, the band should feel secure without being painful, and the cups should contain tissue without gaping or spilling. Because these signs are easier to evaluate after getting a reasonable starting size, calculators are especially useful for first-time sizing, post-weight-change reassessment, and online purchases.
Best practices for measuring at home
- Use a soft measuring tape and keep it level all the way around the body.
- Measure while standing naturally, not holding your breath or expanding the ribcage.
- For underbust, keep the tape snug and firm, directly beneath the bust.
- For full bust, measure around the fullest point without compressing breast tissue.
- Wear a non-padded bra or a thin, unlined bra for more neutral measurements.
- Repeat each measurement once or twice to reduce simple tape placement errors.
Understanding band size
The band size forms the anchor of bra support. In US and UK labeling, the band is usually displayed as an even number such as 30, 32, 34, 36, or 38. In many EU systems, band values are often shown in increments like 65, 70, 75, 80, and 85. This calculator converts your underbust to a recommended band by rounding to a practical even size in inches, then translating that result into the selected system.
Some people prefer a slightly firmer feel for stronger support, especially in high-impact or fuller-bust situations. Others prefer a more forgiving fit for all-day comfort. That is why this calculator includes a fit preference option. A firmer preference slightly lowers the adjusted underbust before rounding, and a comfort preference slightly increases it. This approach does not replace trying on bras, but it can align the estimate with how you prefer the band to feel.
Understanding cup size
Cup size is not absolute. A D cup on a smaller band is not the same volume as a D cup on a larger band. Cup letters depend on the band because bra sizing is a combination measurement. In practical fitting systems, each increase in band size changes the associated cup volume at a given letter. This is also why sister sizing exists, where different band and cup combinations may have similar cup volume, such as 34C and 36B.
This calculator estimates cup size by subtracting the underbust from the full bust and mapping the difference to common cup progressions. For US sizes, the progression often includes A, B, C, D, DD, DDD, G, H, and beyond. For UK sizes, the sequence often includes D, DD, E, F, FF, G, GG, H, HH, and so forth. For EU systems, cup labeling may vary by brand, but many use a progression closer to A, B, C, D, E, F, G, H, and beyond. Because brand conventions differ, exact letters may vary when you compare labels from different manufacturers.
| Bust minus underbust difference | Typical US cup | Typical UK cup | Typical EU cup |
|---|---|---|---|
| 1 inch | A | A | A |
| 2 inches | B | B | B |
| 3 inches | C | C | C |
| 4 inches | D | D | D |
| 5 inches | DD | DD | E |
| 6 inches | DDD or F | E | F |
| 7 inches | G | F | G |
| 8 inches | H | FF | H |
Real-world sizing variation and statistics
Bra sizing variation is a major reason calculators remain valuable. There is no single universal size standard enforced across all brands and product categories worldwide. In the United States, apparel product information is regulated in areas such as labeling and fiber content, but fit dimensions themselves are not fully uniform across the market. In practice, shoppers often compare size guides brand by brand. This is one reason online retailers publish fit notes, customer reviews, and product-specific guidance.
Population data also shows that body dimensions vary widely, which naturally affects bra sizing distribution. Government anthropometric research and public health data are useful for understanding broad body measurement ranges, even if they do not define bra sizes directly. They show why a one-size-fits-all fit assumption is unrealistic and why personalized measurement is more useful than guessing from clothing size alone.
| Reference source | Relevant statistic or takeaway | Why it matters for bra sizing |
|---|---|---|
| CDC anthropometric and body measurement datasets | Adult body dimensions vary substantially across age groups and populations. | Supports the need for actual body measurement instead of guessing by dress size alone. |
| NIST sizing and body measurement research | Standardization efforts show that apparel sizing systems rely on ranges rather than exact body matches. | Explains why two brands can label similar fits differently. |
| University and extension textile programs | Fit education emphasizes comfort, support, garment ease, and style-specific adjustments. | Reinforces that the calculated size is a starting point, not the only possible fit. |
Step-by-step guide to using this bra size calculator
- Select your preferred measurement unit, either inches or centimeters.
- Choose the size system you want to see, such as US, UK, or EU.
- Enter your snug underbust measurement.
- Enter your full bust measurement.
- Choose a fit preference if you want a slightly firmer or more comfortable band feel.
- Choose how the band should be rounded. Most users do best with nearest even band.
- Click the calculate button to see your recommended size, sister sizes, and a visual chart.
Common fitting problems and what they usually mean
Band rides up in the back
This usually suggests the band is too large or has lost elasticity. Try a smaller band and possibly a larger cup letter to maintain cup volume if needed.
Straps dig into shoulders
Many people think tighter straps create better support, but the band should carry most of the support. Digging straps often point to a band that is too loose or cups that do not distribute tissue properly.
Spillage at the top or sides
This often indicates the cups are too small, the style is too closed at the neckline, or the wire shape does not match the body. A larger cup or a different style can help.
Gapping in the cups
Gapping does not always mean the cups are too large. It may happen when the band is too loose, the cups are the wrong shape, or the bra style is too tall for the wearer. Plunge or balconette styles may fit better depending on shape.
Sister sizes explained
Sister sizes are nearby bra sizes with similar cup volume but different band lengths. If your calculated size feels close but not perfect, trying a sister size can be useful. For example, if 34D feels too tight in the band but the cups are good, 36C may be worth trying. If 34D feels too loose in the band but the cup volume seems right, 32DD might be worth exploring. This is particularly helpful because some brands run tight or loose in the band, and some fabrics stretch more than others.
US vs UK vs EU bra sizes
One source of confusion is that cup letters do not align perfectly across global systems. UK sizing often includes doubled letters such as FF, GG, and HH, while US sizing often uses DD, DDD, then moves to G and H, depending on brand. EU systems may use a simpler progression of single letters, though brand-level differences remain common. That means a shopper moving between international retailers should always check the size chart, not just the letter alone.
This calculator helps by showing a recommended size in the selected system, but it is still wise to compare the result against a brand’s own fit guide. If the retailer provides both centimeter and inch charts, use your actual measurements rather than assuming a direct label conversion.
When to remeasure
- After noticeable weight change
- After pregnancy or nursing changes
- If your current bras feel uncomfortable or unsupportive
- If you switch between everyday, sports, strapless, or specialty bra styles
- If you have not measured in the last 6 to 12 months
Authoritative resources for body measurement and apparel fit
If you want to explore body measurement standards, population data, and textile education further, these sources are excellent starting points:
- CDC body measurements and anthropometric data
- NIST apparel sizing and body measurement research
- University of Idaho clothing and textiles education resources
Final expert advice
A bra size calculator is best used as a smart first estimate. It can dramatically reduce trial and error, especially when you are shopping online, changing brands, or reassessing your size after body changes. However, no calculator can fully account for breast shape, root width, projection, asymmetry, tissue softness, or style-specific construction. If your recommended size feels close but not perfect, use fit clues and sister sizes to fine-tune the result.
The most successful approach is to combine accurate measurements, a reliable calculator, and practical fitting awareness. Start with the recommendation on this page, compare it with the brand chart, and evaluate the fit on the body. That method consistently leads to better comfort, support, and confidence than guessing from your current bra label or clothing size alone.
Note: This calculator is an educational sizing tool and does not replace a professional fitting. Bra fit can vary meaningfully by brand, style, and fabric stretch.