Bra Size Calculator
Find your estimated bra size using your underbust and bust measurements. This calculator uses standard sizing guidelines to help you discover your perfect fit. Results are for educational purposes and professional fitting is always recommended.
Your Bra Size Results
Calculation completeInternational Size Equivalents
Sister Sizes (Same Cup Volume)
- —
Different brands may fit differently. Professional fitting is recommended for the best fit.
| Difference (in) | Cup Size |
|---|---|
| 0 | AA |
| 1 | A |
| 2 | B |
| 3 | C |
| 4 | D |
| 5 | DD/E |
| 6 | DDD/F |
| 7 | G |
| 8 | H |
| 9 | I |
| 10 | J |
What this means
Your estimated bra size is based on your underbust and bust measurements.
Explore more style & health tools: Body Shape Calculator · Ideal Weight Calculator · BMI Calculator · Body Fat Calculator
How This Calculator Works
This calculator determines your bra size using the standard method:
Band Size is your underbust measurement, rounded to the nearest even number (e.g., 30, 32, 34).
Cup Size is calculated from the difference between your bust and band measurements:
Band Size = Round(Underbust) to nearest even number
Cup Size = Difference (Bust - Band) mapped to cup letters
For example, if your underbust is 30.5" and your bust is 35", your band is 32" and the 3" difference gives a C cup → 32C.
For a complete body assessment, combine with our Body Shape Calculator or Ideal Weight Calculator.
Real Examples
See where you fall compared to these examples. For a complete body assessment, try our Body Shape Calculator or Ideal Weight Calculator.
Who Can Use This Tool?
This calculator is designed for adults seeking an estimated bra size. It is suitable for:
- • Women looking for a starting point for bra fitting
- • Online shoppers between sizes
- • Educational purposes to understand sizing
Note: This is an estimate. Professional fitting is recommended for the best fit.
Limitations
Bra sizing can vary significantly between brands, styles, and countries. This calculator provides a standard US/UK estimate and may not account for:
- • Different brand sizing systems (EU, FR, etc.)
- • Breast shape variations
- • Weight fluctuations or pregnancy
- • Specific style recommendations (plunge, balconette, etc.)
For a more comprehensive body measurement tool, try our Body Shape Calculator or Body Fat Calculator.
References
The educational information on this page is based on standard bra sizing guidelines from industry experts.
- International Association of Bra Fitters – Sizing Standards
- US Bra Sizing Guidelines – Industry Standards
- European Sizing Conversion Charts
References were selected from recognized industry sources and are reviewed periodically for accuracy.
Trust & Privacy
This calculator is based on publicly available sizing guidelines and is intended for educational purposes.
Editorial Process
The CalculatorKits editorial team reviews this calculator periodically. Review includes:
- • Formula accuracy
- • Sizing classifications
- • Educational content
- • User guidance
Last reviewed: July 2026
Frequently Asked Questions
Measure snugly around your ribcage, directly under your bust. Keep the tape level and breathe normally. Round to the nearest whole number, then round up to the next even number for your band size. For a complete body assessment, try our Body Shape Calculator.
Sister sizes have the same cup volume but different band sizes. For example, 34C and 36B have the same cup volume. This helps when a specific size isn't available or for different brand fits.
This calculator provides a standard US/UK sizing estimate. Different brands may use different sizing systems (EU, FR, etc.) and styles may fit differently. Professional fitting is always recommended.
Simply select the "Centimeters" option before entering your measurements. The calculator will automatically convert them to inches for the sizing calculation.
This is a great starting point for online shopping! However, always check the brand's specific size guide as sizing can vary. Consider ordering multiple sizes if possible.
Body shape can affect how a bra fits. Different breast shapes and chest widths may require different styles. Use our Body Shape Calculator to understand your body type better.
📍 © 2026 CalculatorKits — Bra Size Calculator · For educational use only
Bra Size Calculator: Find Your Band and Cup Size
Finding a comfortable bra can be surprisingly difficult. A size that fits well in one brand may feel different in another, and your size can also change as your body changes. A Bra Size Calculator gives you a convenient starting point by using two basic measurements: your underbust and full bust.
The CalculatorKits tool is designed to make bra sizing easier at home. It uses your measurements to estimate your band size, cup size, international size equivalents, and sister sizes.
The important thing to remember is that a calculated bra size is an estimate. Brand sizing, bra style, fabric, underwire shape, and breast shape can all affect the final fit.
This guide explains how the CalculatorKits Bra Size Calculator works, how to measure yourself correctly, how band and cup sizes are determined, what sister sizes mean, and what to do when your calculated size does not feel right.
Quick Answer
A Bra Size Calculator estimates your bra size using your underbust and full bust measurements.
The CalculatorKits tool allows you to choose inches or centimeters and then enter:
- Underbust measurement
- Bust measurement
The calculator uses the underbust measurement to estimate your band size. It then compares the bust measurement with the calculated band size to determine the cup.
For example:
Underbust: 30.5 inches
Bust: 35 inches
The band is rounded to 32 inches.
The difference is:
35 − 32 = 3 inches
Using the CalculatorKits sizing method, a 3 inch difference corresponds to a C cup.
Estimated size:
32C
The tool also provides international size equivalents and sister size suggestions.
The result is a useful starting point, but it does not guarantee that every bra labelled with that size will fit exactly the same way.
What Is a Bra Size Calculator?
A Bra Size Calculator is an online tool that estimates your bra size from body measurements.
A typical bra size has two parts.
The first part is the band size, such as 30, 32, 34, or 36. This relates to the measurement around your ribcage beneath your bust.
The second part is the cup size, such as A, B, C, D, or DD. The cup is determined in relation to the band size and the difference between your bust and underbust measurements.
This is why a cup letter cannot be considered by itself.
For example, 32C and 36C are not the same size in terms of overall cup volume. This is also why sister sizes are useful when a particular band or cup does not fit comfortably.
The CalculatorKits tool simplifies this process so you can get a starting size without performing the calculations yourself.
Why Use a Bra Size Calculator?
Your bra size is not necessarily permanent.
Weight changes, pregnancy, breastfeeding, hormonal changes, aging, and other changes in your body can affect your measurements.
A Bra Size Calculator can be useful when:
- You are buying a bra online
- Your current bras no longer feel comfortable
- You have gained or lost weight
- You have not measured your size recently
- You are between sizes
- You are buying from an international brand
- You want to check your measurements privately at home
The calculator can narrow down your likely size before you begin shopping.
It can also help explain why your old bra size may no longer be the best match.
If you are interested in other body measurements, the Body Shape Calculator provides additional information about general body proportions.
How Does the Bra Size Calculator Work?
The CalculatorKits method uses your underbust and bust measurements.
Step 1: Calculate the Band Size
The underbust measurement is taken around your ribcage directly below your bust.
CalculatorKits rounds the measurement to the nearest whole number and then uses the next even number for the band size.
For example:
Underbust: 30.5 inches
Estimated band: 32
Another example:
Underbust: 33 inches
Estimated band: 34
The band provides much of the support in a bra, so getting this measurement reasonably accurate is important.
Step 2: Calculate the Cup Size
The calculator compares your bust measurement with the calculated band size.
The CalculatorKits method uses this approximate mapping:
| Difference | Cup |
|---|---|
| 0 inches | AA |
| 1 inch | A |
| 2 inches | B |
| 3 inches | C |
| 4 inches | D |
| 5 inches | DD or E |
| 6 inches | DDD or F |
| 7 inches | G |
| 8 inches | H |
| 9 inches | I |
| 10 inches | J |
For example:
Bust: 36 inches
Band: 32
Difference: 4 inches
Estimated size: 32D
This is the basic calculation performed by the CalculatorKits tool.
How to Use the Bra Size Calculator
The CalculatorKits interface is simple to use.
- Select your preferred measurement unit. Choose inches or centimeters.
- Measure your underbust. Place the measuring tape around your ribcage directly below your bust.
- Measure your bust. Wrap the tape around the fullest part of your bust.
- Enter your underbust measurement in the band measurement field.
- Enter your bust measurement in the bust field.
- Check that your measurements use the correct unit.
- Click Calculate My Bra Size.
- Review your estimated band and cup size.
- Check the international size equivalents if you are shopping from a brand that uses another sizing system.
- Review the sister sizes provided by the calculator.
- Compare your result with the specific size guide provided by the brand before ordering.
Accurate measurements are the most important part of the process.
How to Measure Your Underbust Correctly
The underbust measurement is taken around your ribcage directly beneath your bust.
Use a soft, flexible measuring tape.
Stand naturally.
Wrap the tape around your body.
Make sure the tape remains level around your back.
Keep the tape snug without pulling it painfully tight.
Breathe normally while measuring.
Do not hold your breath or deliberately push your chest outward.
A loose measurement can produce a band that is too large, while an excessively tight measurement can produce a band that is too small.
The goal is to get a realistic measurement of your ribcage.
How to Measure Your Bust Correctly
The bust measurement should be taken around the fullest part of your bust.
Place the tape around your body and keep it level.
The tape should rest comfortably without compressing the breast tissue.
For the most consistent measurement, CalculatorKits recommends using a non padded bra if you are wearing one.
Heavy padding can change the measurement and make the calculator estimate less representative of your actual size.
Take the measurement more than once if you are uncertain about the number.
What If Your Measurements Are in Centimeters?
You do not need to convert centimeters manually.
Select Centimeters in the CalculatorKits tool and enter your measurements.
The calculator performs the conversion needed for its sizing calculation.
This is useful for users who normally measure in centimeters.
Always confirm that centimeters are selected before entering the values.
Entering a centimeter measurement while inches are selected can produce an incorrect result.
What Does the Band Size Mean?
The band is the number in your bra size.
Examples include:
30C
32D
34B
36C
The band sits around your ribcage and provides much of the support.
A well fitting band should feel secure but comfortable.
It should not constantly move upward at the back.
It should not cause significant pain or restrict comfortable breathing.
It should also not be so loose that it shifts substantially when you move.
If the band rides up your back, the band may be too loose.
If it feels excessively tight, another band size may be more comfortable.
What Does the Cup Size Mean?
The cup is represented by a letter.
Examples include:
A
B
C
D
DD
DDD
The cup represents breast volume relative to the band.
This means the letter should never be considered by itself.
For example, 32C and 34C have different band sizes and different overall cup volumes.
This is one reason that changing the band size often means changing the cup letter as well.
What Are Sister Sizes?
Sister sizes are bra sizes with different band sizes but similar overall cup capacity.
For example:
34C can have sister sizes such as 32D and 36B.
The smaller band is paired with a larger cup letter.
The larger band is paired with a smaller cup letter.
Sister sizes can be helpful when your calculated cup feels close but the band does not feel comfortable.
The CalculatorKits tool provides sister size suggestions to help with this process.
However, sister sizes are not guaranteed to fit identically.
Changing the band size can also change the way the underwire, cups, and straps sit on your body.
What If Your Calculated Bra Size Does Not Fit?
A calculator gives you a starting size, not a guarantee.
Start by checking the band.
If the band rides upward at the back, it may be too loose.
If the band digs painfully into your ribs, another size may work better.
Then check the cups.
If breast tissue spills over the top or sides, the cup may be too small.
If the cup has significant gaping, the cup may be too large, although the bra style could also be causing the problem.
A different style can fit very differently even when the size label is identical.
Common Signs of a Poor Bra Fit
Your bra may not be fitting correctly if:
- The band rides up your back
- The band feels painfully tight
- Breast tissue spills out of the cups
- The cups have significant empty space
- The underwire sits on breast tissue
- The center of the bra feels uncomfortable
- Straps constantly fall off
- Straps dig into your shoulders
- Cups move when you move
- You feel uncomfortable after wearing the bra for a short period
These signs do not always mean that you need an entirely different size.
The problem can sometimes be the bra style, material, or shape.
Why Breast Shape Matters
Measurements are important, but they do not describe the complete shape of your breasts.
Two people can have the same underbust and bust measurements while preferring completely different bra styles.
Breast fullness, root width, projection, and other shape characteristics can influence how a cup fits.
This is why a calculated size should be considered a starting point.
For example, a balconette, plunge, full coverage, and sports bra can all fit differently on the same person.
The CalculatorKits result helps narrow down the size, while the physical fit helps determine whether a particular bra works for you.
Why Can Different Bra Size Calculators Give Different Results?
Bra sizing is not completely standardized worldwide.
Different brands may use different band rounding rules.
Cup progressions can vary.
US, UK, EU, and other sizing systems use different labels.
Some brands may also adjust sizing depending on the style of the bra.
As a result, two calculators can give different answers even when you enter the same measurements.
That does not automatically mean one calculator is wrong.
The important thing is to understand the calculation method being used.
Always check the size chart of the specific brand you plan to buy.
US, UK, EU, and AU Bra Sizes
The same general bra size can have different labels in different countries.
For example, a US or UK band might use a number such as 34, while an EU band might use a number such as 75.
Cup lettering can also vary between systems.
Because international conversions are not perfectly uniform, the CalculatorKits international equivalents should be considered a starting reference.
When purchasing an international brand, check the manufacturer’s own chart before placing an order.
Should You Measure Over a Bra?
A non padded bra is generally preferable if you want to wear a bra while measuring.
Heavy padding can add volume and change the bust measurement.
The CalculatorKits instructions recommend using a non padded bra when possible.
You can also measure without a bra if that gives you a comfortable and consistent measurement.
The most important thing is to avoid additional padding that changes your natural measurements.
Does Bra Size Change Over Time?
Yes.
Your measurements can change for many reasons.
These can include:
• Weight gain
• Weight loss
• Pregnancy
• Breastfeeding
• Hormonal changes
• Menopause
• Aging
• Changes in body composition
This is why it is not a good idea to assume that a bra size you wore several years ago is still correct today.
A new measurement can save time and make online shopping easier.
How Often Should You Recalculate Your Bra Size?
There is no need to calculate your size every week.
A better approach is to measure again when there is a meaningful reason.
Consider checking your size when:
• Your body weight changes noticeably
• Your existing bras become uncomfortable
• You have gone through pregnancy or breastfeeding
• Your body shape has changed
• You are shopping for new bras after a long period
• Your usual size no longer fits as expected
If your current bras remain comfortable and your measurements have not changed, there is usually no reason to repeatedly calculate your size.
Using a Bra Size Calculator for Online Shopping
A Bra Size Calculator can be particularly useful when shopping online.
Start with accurate measurements.
Then:
- Calculate your estimated size.
- Check the brand’s size chart.
- Confirm whether the brand uses US, UK, EU, or another sizing system.
- Read the product’s fit notes.
- Consider the style of the bra.
- Check the return or exchange policy.
- Order based on the brand’s information rather than the calculator alone.
This approach reduces the chance of ordering the wrong size.
Can a Bra Size Calculator Replace a Professional Fitting?
Not completely.
A professional fitting can evaluate the actual behavior of a bra on your body.
A fitter can look at the band, cups, straps, underwire, and overall comfort.
A calculator cannot physically assess those things.
That said, a good Bra Size Calculator is still useful because it gives you an informed starting point.
This is especially helpful when ordering online or when you want to measure yourself privately at home.
Common Bra Measurement Mistakes
Pulling the Tape Too Tight
The measuring tape should be snug but comfortable.
Letting the Tape Slope
Keep the tape level around your body.
Measuring Over Thick Clothing
Clothing can add unnecessary measurement.
Wearing Heavy Padding
Padding can increase the bust measurement.
Holding Your Breath
Breathe naturally while measuring.
Measuring the Wrong Part of the Bust
Use the fullest part of the bust.
Entering the Wrong Unit
Check whether the calculator is set to inches or centimeters.
Focusing Only on the Size Label
Actual fit is more important than the number printed on the tag.
How Accurate Is a Bra Size Calculator?
A Bra Size Calculator can provide a consistent estimate when measurements are entered correctly.
However, it cannot account for every factor affecting bra fit.
Important variables include:
• Brand sizing
• Bra style
• Breast shape
• Underwire design
• Fabric stretch
• Strap placement
• International sizing standards
This means the calculator is best used as a starting point.
The CalculatorKits result can help narrow down your likely size, but the final test is how the actual bra fits and feels.
Privacy and Personal Measurements
Measurements related to bra sizing are personal.
The CalculatorKits page states that its calculations are performed locally in the browser and that the tool does not require an account.
This allows users to calculate their estimated size without creating an account.
As with any online service, you should review the current privacy information if you have specific privacy concerns.
Frequently Asked Questions
What is a Bra Size Calculator?
A Bra Size Calculator estimates your band and cup size from your underbust and bust measurements.
What measurements do I need?
You need your underbust measurement and your full bust measurement.
How does the calculator determine the band size?
CalculatorKits uses your underbust measurement, rounds it according to its sizing method, and uses the resulting even number as the estimated band size.
How does the calculator determine cup size?
The calculator compares the bust measurement with the calculated band size and uses the difference to determine the cup letter.
Can I use centimeters?
Yes. The CalculatorKits tool supports both inches and centimeters.
Should I wear a bra while measuring?
A non padded bra can be used. Heavy padding may change the bust measurement.
Should the tape be tight?
The tape should be snug and level but should not compress the body excessively.
What is a sister size?
A sister size has a different band size but similar overall cup capacity. For example, 34C may have sister sizes such as 32D or 36B.
Why is my calculated size different from my usual size?
Your body measurements may have changed, or your usual brand may use a different sizing system.
Why do different brands fit differently?
Brands can use different sizing standards, fabrics, cup shapes, and underwire designs.
Does breast shape affect fit?
Yes. Two people with the same measurements may prefer different bra styles because breast shape can influence how the cups fit.
Can my bra size change after weight loss?
Yes. Weight changes can alter your underbust and bust measurements.
Can pregnancy affect bra size?
Yes. Pregnancy and breastfeeding can change breast size and shape.
Should I always buy the size shown by the calculator?
Use it as a starting point. Always compare it with the brand’s own size chart.
How often should I measure my bra size?
Measure again when your body changes noticeably or your current bras stop fitting comfortably.
Can a Bra Size Calculator guarantee a perfect fit?
No. It provides an estimate based on measurements. Actual fit also depends on the brand, style, fabric, and breast shape.
Key Takeaways
A Bra Size Calculator provides a convenient starting point for estimating your band and cup size.
The CalculatorKits method uses:
- Underbust measurement
- Full bust measurement
The underbust measurement is used to estimate the band.
The difference between bust and band measurements is used to estimate the cup.
The tool supports inches and centimeters and provides international size equivalents and sister sizes.
Your calculated size may not fit identically across every brand.
Breast shape and bra style can also affect fit.
For the best result, measure carefully, keep the tape level, use a non padded bra when possible, and check the manufacturer’s size chart before buying.
Related CalculatorKits Tools
Body Shape Calculator
Explore general body proportions using several body measurements. This can provide additional context when learning about body measurements and clothing fit.
BMI Calculator
Calculate BMI from height and weight and review the standard adult BMI categories. This provides general body size information rather than clothing measurements.
Body Fat Calculator
Estimate body fat percentage using body measurements. This provides a different perspective on body composition.
Ideal Weight Calculator
Compare your height with several traditional ideal weight formulas and explore different approaches to estimating body weight.
References
- Wacoal Bra Fit Calculator
Provides practical guidance for measuring underbust and bust size and explains basic bra fitting principles.
Wacoal: Bra Fit Calculator - Wacoal 5 Points of Fit
Explains how band position, straps, cups, shape, and lift affect bra fit.
Wacoal: 5 Points of Fit - Wacoal Breast Shape Guide
Explains why breast shape can affect bra style and fit in addition to size.
Wacoal: Breast Shape Guide - Victoria’s Secret Bra and Bralette Size Guide
Provides bra measurement and sizing guidance for shoppers.
Victoria’s Secret: Bra Size Guide - Frimley Health NHS Foundation Trust, Bra Measurement
Provides practical information about measuring bra size and factors that can affect breast measurements over time.
Frimley Health NHS: Bra Measurement - NHS, Breast Pain
Provides general information about breast pain and when medical advice may be appropriate.
NHS: Breast Pain
Medical Disclaimer
This article and the CalculatorKits Bra Size Calculator are provided for general educational and informational purposes only. Bra sizing is not a medical assessment and cannot diagnose the cause of breast pain, breast changes, or other symptoms. If you notice a new breast lump, persistent pain, unusual discharge, skin changes, or another concerning change, consult a qualified healthcare professional.
Written and reviewed by the CalculatorKits Editorial Team
Last Updated: September 6, 2026