Find your perfect bra size with US, UK, and EU sizing systems
Powered by Toolraxy
Founder & CEO, Toolraxy
Faiq Ur Rahman is a web designer, digital product developer, and founder of Toolraxy, a growing platform of web-based calculators and utility tools. He specializes in building structured, user-friendly tools focused on health, finance, productivity, and everyday problem-solving.
User Ratings:
ADVERTISEMENT
ADVERTISEMENT
Finding a well-fitting bra is a common challenge, with studies suggesting a large percentage of women wear the wrong size without realizing it. A bra size calculator is an essential tool for demystifying the sizing process and helping you determine your correct band and cup size from the comfort of your home. This tool is designed for anyone who wants to check their current size, shop online with confidence, or understand how bra sizing works across different international systems. By simply inputting two key measurements, your underbust and overbust, you can instantly receive your recommended size in US, UK, or EU formats, along with helpful information like sister sizes and fit tips.
Measure Your Underbust:Β Using a soft measuring tape, measure snugly around your ribcage, directly under your bust.
Measure Your Overbust:Β Measure around the fullest part of your bust, keeping the tape parallel to the floor.
Enter Your Measurements:Β Type both numbers into the calculator and select the correct unit (inches or centimeters).
Choose a Sizing System:Β Select your preferred standard:Β US/Canada,Β UK/Australia, orΒ EU.
Set Your Fit Preference:Β Indicate if you prefer a snug, normal, or loose band fit.
View Your Results:Β The calculator will instantly display your band size, cup size, sister sizes, and international size equivalents.
This tool uses a two-part calculation to determine your bra size. First, it establishes your band size from your underbust measurement. Second, it calculates your cup size based on the difference between your overbust and underbust measurements.
Core Logic:
The calculation is based on standard bra-fitting principles. Your band size is a derived from your underbust measurement, and your cup size represents the volumetric difference between your bust and your ribcage.
The primary formulas are as follows:
Band Size Calculation:
The underbust measurement (converted to inches if necessary) is rounded to the nearest whole number.
If the result is an odd number, it is increased by 1 to make it even (e.g., a 31″ underbust results in a band size of 32).
This number is then adjusted based on theΒ Fit PreferenceΒ setting:
Snug fit: Band Size - 1
Normal fit: Band Size (no change)
Loose fit: Band Size + 1
A minimum band size of 28 is enforced.
Cup Size Calculation:
Difference = Overbust - UnderbustΒ (both in inches)
This difference is then mapped to a cup size index. For example:
Difference of 0.5″ to 1.4″ β Index 1 (A cup)
Difference of 1.5″ to 2.4″ β Index 2 (B cup)
Difference of 2.5″ to 3.4″ β Index 3 (C cup)
(This pattern continues, with each full inch of difference corresponding to the next cup size.)
Sizing System Logic:
The cup size index is applied to a system-specific array. The UK system uses its unique sequence (e.g., D, DD, E, F, FF) while the US and EU systems use a simpler progression (e.g., D, DD, DDD, G, H).
Validation and Edge Cases:
If either the underbust or overbust value is zero or negative, the tool will prompt the user to enter valid measurements.
The cup size index is capped at the maximum size available in the selected system’s array.
Sister sizes are calculated by adjusting the band size by Β±2 and moving one cup size in the opposite direction (e.g., down a band, up a cup).
Let’s illustrate the process with a common set of measurements.
Scenario:Β You measure your underbust at 32 inches and your overbust at 38 inches. You want to find your size in the UK sizing system.
Steps and Results:
Enter Measurements:Β InputΒ 32Β for Underbust andΒ 38Β for Overbust, both in inches.
Select System:Β ChooseΒ “UK / Australia”Β from the sizing system dropdown.
Set Fit:Β Keep the fit preference atΒ “Normal”.
Interpretation:Β The results section now displays:
Band Size:Β 32 in
Cup Size:Β E
Your Bra Size:Β 32E
Sister Sizes:Β 30FΒ andΒ 34DD
Size Equivalents:Β US: 32DDD,Β UK: 32E,Β EU: 32F
Takeaway:Β The calculator has determined your size by taking the 6-inch difference between your measurements. In the UK system, a 6-inch difference corresponds to an E cup. The tool has also provided your sister sizes and international equivalents, giving you a complete picture for shopping.
How accurate is this bra size calculator?
This calculator is a highly reliable starting point for finding your size, as it uses the standard industry formulas based on the difference between your underbust and overbust measurements. However, it should be used as a guide, as the final fit can vary by brand and style.
Can I use this tool to convert between different sizing systems?
Yes, absolutely. By calculating your size and then switching the “Sizing System” dropdown, you can see your equivalent size in US, UK, and EU standards. The tool also displays these equivalents in the results section.
What causes my calculated size to feel too tight?
A feeling of tightness is often caused by theΒ cup sizeΒ being too small, not the band. If the cup is too small, breast tissue can push the band away, making it feel tight. Trying a larger cup size with the same band can often resolve this issue.
Is this tool safe and private to use?
Yes, it is completely safe and private. The calculator is a client-side tool, meaning all calculations are performed locally in your web browser. Your personal measurements are never transmitted, processed, or stored on any server.
What is the difference between a sister size and a true size?
AΒ true sizeΒ is the calculated size that should fit you best. AΒ sister sizeΒ is an alternative size where the cup volume remains the same, but the band size is different. For example, if your true size is 34E, a sister size is 36DD. They can be useful for finding a better fit in brands that run small or large.
Can I use this calculator for all types of bras?
Yes, the calculator provides a baseline size that applies to most bra types, including everyday, sports, and strapless bras. However, some specific styles, like high-impact sports bras, may have their own sizing quirks and you may need to adjust slightly.
Does the tool provide a price estimate for bras?
While the tool includes a currency selector for potential future features, its primary function is to provide accurate size calculations. It does not provide price estimates based on bra size or style.
Why does the tool ask for a fit preference?
The fit preference is included to personalize the final band size calculation. Some people prefer a tighter, more supportive band (snug), while others prefer a more relaxed fit. This setting allows the calculator to adjust the final band size recommendation accordingly.
ADVERTISEMENT
ADVERTISEMENT
