My Bra Size Calculator
Finding the right bra size can be surprisingly difficult. Different brands, countries, materials, and bra styles can all affect how the same labeled size fits. Measuring yourself at home can provide a useful starting point, especially when shopping online or comparing sizing systems.
The My Bra Size Calculator helps estimate your bra size using two measurements: your band measurement and your bust measurement. You can also select a sizing system and choose whether you prefer a standard, snug, or loose fit.
In addition to your estimated bra size, the calculator provides your band size, cup size, bust-to-band difference, sister sizes, and alternate cup sizes. These extra results can be useful when a particular bra feels too tight, too loose, or doesn’t fit correctly in the cup.
The result should be considered a starting point rather than a guarantee of fit, since bra sizing varies considerably among manufacturers.
What Is the My Bra Size Calculator?
The My Bra Size Calculator is an online bra-sizing tool that estimates a bra size from:
- Band measurement
- Bust measurement
- Sizing system
- Fit preference
The calculator supports five sizing systems:
- US
- UK
- European
- Australian
- French
It also offers three fit preferences:
- Standard Fit
- Snug Fit
- Loose Fit
Once you enter your measurements, the calculator determines an estimated band size and cup size and combines them into a bra-size result.
Measurements You Need
You only need two physical measurements to use the calculator.
Band Measurement
The band measurement represents the measurement around your body underneath the bust.
The calculator expects this measurement in inches.
For the most useful result, the measuring tape should be positioned horizontally around the body and held snugly without digging into the skin.
For example:
Band measurement = 32 inches
Bust Measurement
The bust measurement is taken around the fullest part of the bust.
Again, the calculator expects inches.
For example:
Bust measurement = 36 inches
The calculator requires the bust measurement to be equal to or greater than the band measurement.
How to Use the My Bra Size Calculator
Step 1: Measure Your Band
Use a flexible measuring tape around your rib cage directly underneath your bust.
Keep the tape level around your body and enter the result in inches.
Step 2: Measure Your Bust
Measure around the fullest part of your bust while keeping the tape level.
Don’t pull the tape excessively tight.
Enter that measurement in inches.
Step 3: Select Your Sizing System
Choose the system you want to use:
- US Sizing
- UK Sizing
- European Sizing
- Australian Sizing
- French Sizing
This matters because different regions use different band-number conventions and cup-letter systems.
Step 4: Select Your Fit Preference
The calculator offers:
Standard Fit: Uses the calculated band size without a fit adjustment.
Snug Fit: Applies a -2 adjustment to the calculated band size.
Loose Fit: Applies a +2 adjustment to the calculated band size.
These adjustments are calculator-specific estimates and don’t necessarily correspond to how every bra brand defines a snug or loose fit.
Step 5: Calculate
Click Calculate to see your estimated bra size and additional sizing information.
Understanding Your Results
The calculator provides six results.
Your Bra Size
This combines the estimated band number with the calculated cup size.
For example:
34C
The number represents the band size, while the letter represents the cup size.
Band Size
This is the calculated band measurement after applying the selected sizing system and fit preference.
Cup Size
The calculator estimates the cup letter based on the difference between your bust and band measurements.
Difference
This is the numerical difference between your bust and band measurements:
Bust − Band = Difference
For example:
36 − 32 = 4 inches
The calculator displays the difference to one decimal place.
Sister Sizes
Sister sizes have similar cup volume but different band sizes.
The calculator provides two alternative sizes based on a smaller or larger band and a corresponding cup adjustment.
Alternate Sizes
These results keep the calculated band size but move one step up or down in the calculator’s cup-size sequence.
They can be useful when exploring nearby sizing options, although they don’t necessarily represent equivalent-volume sizes in every sizing system.
How the Cup Size Is Calculated
The calculator first determines the difference between the bust and band measurements.
The formula is:
Cup Difference = Bust Measurement − Band Measurement
For example, if your measurements are:
- Band = 32 inches
- Bust = 36 inches
then:
36 − 32 = 4 inches
The calculator rounds this difference to the nearest whole number and uses that number as an index in its cup-size scale.
Its cup-size sequence is:
AA, A, B, C, D, DD/E, DDD/F, G, GG, H, HH, J, JJ, K
Because the calculator uses a predefined sequence, the resulting cup designation is an estimate rather than a universal conversion.
How Band Size Is Calculated
The band calculation depends on the selected sizing system.
US, UK, and Australian Sizing
For US, UK, and Australian sizing, the calculator first rounds the band measurement to a whole number.
If the rounded number is odd, it increases it by one to produce an even number.
It then adds 4 and applies the selected fit adjustment.
For example, with a 31-inch band measurement and standard fit:
- Round 31 to 31
- Adjust to the next even number: 32
- Add 4: 36
- Standard fit adds 0
The estimated band is therefore:
36
European Sizing
For European sizing, the calculator converts the inch measurement to centimeters and rounds to the nearest multiple of 5.
The fit adjustment is then applied.
French Sizing
French sizing converts the band measurement into centimeters and rounds it to a whole number before applying the fit adjustment.
Because regional sizing systems differ, the same underlying body measurements can produce very different-looking size labels.
Worked Example
Suppose someone enters:
- Band measurement: 32 inches
- Bust measurement: 36 inches
- Sizing system: US
- Fit preference: Standard Fit
Step 1: Calculate the Difference
36 − 32 = 4 inches
The calculator uses 4 as the cup-size index.
Based on its cup sequence, index 4 corresponds to:
D
Step 2: Calculate the Band
The band measurement is already an even number:
32
The US/UK/Australian calculation then adds 4:
32 + 4 = 36
Because the selected fit is Standard, there is no additional adjustment.
The calculated band is:
36
Step 3: Combine Band and Cup
The resulting bra size is:
36D
Step 4: Sister Sizes
For non-European/non-French sizing, the calculator uses a band increment of 2.
It calculates nearby sizes by reducing the band by 2 while increasing the cup index, or increasing the band by 2 while decreasing the cup index.
This provides alternative sizes around the calculated result.
The exact displayed sister sizes depend on the cup position in the calculator’s predefined sequence.
What Are Sister Sizes?
Sister sizes are bra sizes with related cup volumes but different band measurements.
For example, a common concept is that moving to a larger band generally requires moving to a smaller cup letter to maintain a similar cup volume.
Conversely, moving to a smaller band generally requires moving to a larger cup letter.
This is useful when you find a bra where:
- The cups fit but the band is too tight.
- The band fits but the cups need a different volume.
- A particular brand runs tighter or looser than expected.
However, sister sizing is not perfectly interchangeable across all brands and sizing systems.
What Are Alternate Sizes?
The calculator also provides two alternate cup sizes while keeping the same band size.
These are simply the adjacent cup entries in its predefined cup-size sequence.
For example, if the calculated cup is C, the calculator can provide the cup immediately before and after C in its sequence.
These alternatives are useful for exploring nearby cup volumes, but they aren’t necessarily equivalent to sister sizes.
The distinction is important:
Sister size: Changes the band and adjusts the cup.
Alternate size: Keeps the band and changes the cup.
Choosing the Correct Sizing System
International bra sizing can be confusing because a size label does not mean exactly the same thing everywhere.
US Sizing
US bra sizing commonly uses numerical band sizes and cup letters such as A, B, C, D, DD, and beyond.
UK Sizing
UK sizing uses its own cup-letter progression, particularly at larger cup sizes.
European Sizing
European sizing generally uses band numbers based on centimeters rather than the numerical system traditionally used in the US and UK.
Australian Sizing
Australian sizing uses its own labeling conventions, which can differ from US and UK labels.
French Sizing
French sizing uses numerical values that differ from standard US/UK band numbers.
Because of these differences, always check the sizing chart provided by the specific brand before buying.
How Fit Preference Changes the Result
The calculator includes a fit-preference setting because people can have different preferences for how snug a bra band feels.
Standard Fit
The calculator makes no additional band adjustment.
This provides the baseline calculated size.
Snug Fit
A 2-inch adjustment is subtracted from the calculated band size.
This produces a smaller band number.
Loose Fit
A 2-inch adjustment is added to the calculated band size.
This produces a larger band number.
These settings are mathematical adjustments within this calculator. They should not be interpreted as standardized industry definitions of snug or loose bra fitting.
Signs That Your Bra May Not Fit Correctly
A calculator provides a starting size, but the actual fit of a bra is often more informative.
Potential signs that a bra isn’t fitting correctly include:
- The band rides up at the back.
- The band feels uncomfortably tight.
- Cups gape significantly.
- Breast tissue spills over the top or sides.
- Underwires sit on breast tissue.
- Straps constantly fall off.
- Straps dig deeply into the shoulders.
- The center portion of the bra does not sit as intended.
Different styles can also fit differently. A molded cup, unlined bra, balconette, plunge, sports bra, and bralette may all feel different even when labeled with the same size.
Tips for Measuring Your Bra Size
Use a Flexible Tape Measure
A flexible measuring tape makes it easier to follow the body’s contours accurately.
Keep the Tape Level
The tape should generally remain horizontal around your torso rather than rising or falling at the back.
Don’t Pull Too Tightly
An excessively tight tape can produce an artificially small measurement.
Measure More Than Once
If you’re uncertain about a measurement, take it again and compare the results.
Check the Brand’s Size Chart
Your calculated size is a useful starting point, but manufacturer charts should be checked before purchasing.
Why Your Calculated Size May Differ From Your Current Bra
There are several possible reasons.
First, different brands may use different sizing conventions.
Second, bras are constructed differently. A structured molded cup can fit differently from a flexible unlined cup even when both carry the same size label.
Third, measurement techniques can vary.
Finally, this calculator uses a simplified mathematical system. Professional bra fitting can involve additional measurements and consideration of breast shape, tissue distribution, and bra construction.
Therefore, a mismatch between the calculator and a bra you already own doesn’t automatically mean one measurement is wrong.
Limitations of the My Bra Size Calculator
The calculator is designed to provide an estimate rather than a guaranteed bra fit.
It uses only:
- Band measurement
- Bust measurement
- Sizing system
- Fit preference
It does not directly account for breast shape, projection, spacing, asymmetry, torso shape, bra style, fabric stretch, or individual brand sizing.
Its cup-size sequence also combines some regional cup labels, meaning that the output should not be interpreted as a universal conversion between all international sizing systems.
For the best fit, use the calculator as a starting point and then compare the result with the manufacturer’s sizing chart and the actual fit of the garment.
Frequently Asked Questions
1. What is the My Bra Size Calculator?
It is an online calculator that estimates your bra size from band and bust measurements while allowing you to select a regional sizing system and fit preference.
2. What measurements do I need?
You need your band measurement and bust measurement, both entered in inches.
3. Where should I measure my band?
Measure around your rib cage directly underneath the bust, keeping the measuring tape level and comfortably snug.
4. Where should I measure my bust?
Measure around the fullest part of the bust while keeping the tape level around your body.
5. Why must my bust measurement be larger than my band measurement?
The calculator uses the difference between the two measurements to estimate cup size. If the bust measurement is smaller, the calculation cannot produce the intended cup-size estimate.
6. Which sizing systems does the calculator support?
It supports US, UK, European, Australian, and French sizing systems.
7. What is a sister size?
A sister size changes the band size while adjusting the cup size in the opposite direction to provide a related cup volume.
8. What does Standard Fit mean?
Standard Fit uses the calculator’s baseline band calculation without an additional snug or loose adjustment.
9. What does Snug Fit do?
The Snug Fit setting subtracts 2 from the calculated band size within the calculator’s formula.
10. What does Loose Fit do?
The Loose Fit setting adds 2 to the calculated band size.
11. Why is my calculated size different from a size I normally wear?
Sizing varies between brands, countries, bra styles, and measurement techniques. Your current size may also have been determined using a different fitting method.
12. Can I use the calculator for online bra shopping?
Yes. It can provide a useful starting point, but you should always compare the result with the specific retailer’s or manufacturer’s size chart.
13. Are sister sizes interchangeable?
Not exactly. Sister sizes are related, but changing the band can alter how the bra feels and how it supports your body.
14. Does cup size have the same meaning in every country?
No. Cup-letter conventions differ among sizing systems, particularly as cup sizes increase. Always check the relevant regional or brand-specific chart.
15. Is the calculator’s result guaranteed to fit?
No. It is an estimate based on measurements and predefined formulas. Actual fit also depends on bra design, brand sizing, breast shape, and personal preference.
Final Thoughts
The My Bra Size Calculator provides a convenient starting point for estimating bra size from two simple measurements. By supporting multiple international sizing systems and offering standard, snug, and loose fit options, it can also help you explore how different sizing approaches affect the final result.
The calculator’s sister-size and alternate-size results are particularly useful when your calculated size doesn’t feel quite right or when you’re comparing different bras.
For the most accurate shopping decision, combine the calculator’s estimate with careful measurements, the manufacturer’s sizing chart, and the actual fit of the bra. Since sizing can vary considerably between brands and styles, the number on the label is only one part of finding a comfortable, supportive fit.