Bra Size Measurement Calculator
Finding the right bra size can be difficult because bra sizing varies between countries, brands, and styles. Our Bra Size Measurement Calculator provides a quick estimate based on your band and bust measurements and lets you select a US/UK, European, or Australian measurement system.
For the best result, take your measurements carefully and use the calculator as a starting point when choosing a bra.
What Is a Bra Size?
A bra size generally consists of two parts:
- Band size: The number representing the measurement around your ribcage beneath your bust.
- Cup size: The letter representing the difference between your bust measurement and band measurement.
For example, a size such as 34C contains a band size of 34 and a cup size of C.
However, cup volume is not identical across every band size. This is why sister sizes can be useful when a particular bra does not fit comfortably.
How to Measure Your Bra Size
You only need two measurements for this calculator: your band measurement and your bust measurement.
1. Measure Your Band
Wrap a soft measuring tape around your torso directly underneath your breasts.
Keep the tape:
- Snug but not painfully tight
- Level around your body
- Parallel to the floor
- Flat against your skin without digging in
Record the measurement in inches if you are using the US/UK or Australian option.
2. Measure Your Bust
Place the measuring tape around the fullest part of your bust.
Do not pull the tape too tightly. Keep it comfortably against your body and make sure the tape remains level.
Record the measurement in inches.
3. Enter Both Measurements
Enter your measurements into the calculator and select the sizing system you want to use.
The calculator will provide an estimated:
- Band size
- Cup size
- Overall bra size
- Sister size down
- Sister size up
How the Bra Size Calculator Works
The calculator compares your bust measurement with your band measurement to estimate the cup size.
The basic idea is:
Bust Measurement − Band Measurement = Cup Difference
A larger difference generally corresponds to a larger cup letter.
The calculator then combines the estimated cup size with the calculated band size to produce your estimated bra size.
Because sizing conventions differ between systems and manufacturers, the result should be treated as an estimate rather than a guarantee of fit.
US/UK Bra Sizing
US and UK bra sizing commonly uses numerical band sizes along with lettered cup sizes.
Depending on the brand, larger cup sizes can be represented differently. For example, some brands use DD, while others may continue with additional letters or use different conventions.
This means that two bras carrying apparently similar sizes may not fit exactly the same way.
European Bra Sizing
European bra sizing generally uses centimeter-based band measurements and different numerical sizing increments.
When selecting the EU option, the calculator converts the entered measurement and estimates an appropriate European band size.
Always check the manufacturer’s size chart when purchasing a bra because individual brands may use slightly different measurements.
Australian Bra Sizing
Australian bra sizing uses its own conventions for band and cup sizes. The calculator includes an Australian option to provide an estimate using the measurement system represented in the calculator.
As with other sizing systems, brand-specific sizing charts can produce different recommendations.
What Are Sister Sizes?
Sister sizes are bra sizes that have a similar cup volume but different band measurements.
For example, if a particular bra feels too tight around the band, you may be able to move to a larger band while moving down a cup letter.
Likewise, if the band feels too loose, you may be able to choose a smaller band and move up a cup letter.
The relationship can be summarized as:
Smaller band + larger cup
or
Larger band + smaller cup
The exact sister-size relationship depends on the sizing system and the particular bra manufacturer.
Why Your Calculated Size May Not Fit Perfectly
A calculator cannot account for every factor that affects bra fit.
Your ideal size may vary because of:
- Brand differences
- Bra style
- Cup shape
- Underwire design
- Fabric stretch
- Breast shape
- Band construction
- Different international sizing standards
- Personal fit preferences
For example, a balconette bra, T-shirt bra, sports bra, and plunge bra can fit differently even when they carry the same labeled size.
Signs Your Bra May Not Fit Correctly
After putting on a bra, check several areas rather than relying only on the label.
Band
The band should sit relatively level around your body. If it rides upward at the back, it may be too loose.
Cups
Your breasts should fit comfortably inside the cups without significant spilling or excessive empty space.
Straps
Straps should provide support without digging deeply into your shoulders.
Underwire
If the bra has underwire, it should generally sit around the breast tissue rather than directly on it.
Center Gore
For many wired bra styles, the center section between the cups should sit comfortably against the chest. The exact fit can vary by breast shape and bra design.
Why Measuring Your Bra Size Is Useful
Regularly checking your measurements can be helpful because body measurements can change over time.
Changes in weight, pregnancy, breastfeeding, exercise, aging, or other normal body changes can affect bra fit.
Measuring yourself before buying a new bra can therefore provide a better starting point than relying on a size you purchased several years ago.
How to Use the Bra Size Calculator
Using the calculator takes only a few steps:
- Measure around your ribcage underneath your bust.
- Measure around the fullest part of your bust.
- Enter the band measurement.
- Enter the bust measurement.
- Select US/UK, EU, or AU.
- Click Calculate.
- Review your estimated band size, cup size, bra size, and sister sizes.
If you want to try a different sizing system, simply change the measurement-system selection and calculate again.
Frequently Asked Questions
Should I wear a bra while measuring?
For the most consistent measurement, use a lightly lined or unpadded bra if you prefer to wear one while measuring. Avoid heavily padded bras because they can add volume and affect the measurement.
Should the measuring tape be tight?
The tape should be snug but should not dig into your skin. Keep it level and avoid pulling it excessively tight.
Why does my bra size differ between brands?
Different manufacturers can use different sizing standards, materials, cup shapes, and patterns. A labeled size is therefore not always identical in fit across brands.
What if my bust measurement is between sizes?
Try measuring again to make sure the tape is positioned correctly. You can also compare the result with the manufacturer’s size chart and consider neighboring sizes.
What are sister sizes used for?
Sister sizes can help when the cup volume seems appropriate but the band feels too tight or too loose. Changing the band size usually requires changing the cup letter in the opposite direction to maintain a similar cup volume.
Is the calculator’s result guaranteed to be my exact size?
No. The calculator provides an estimated size based on the measurements and sizing rules used by the calculator. Actual fit can vary significantly between brands and bra styles.
Final Thoughts
The Bra Size Measurement Calculator is a convenient starting point for estimating your bra size from two basic measurements. Accurate measuring is important, but finding the best-fitting bra also involves considering your shape, the style of the bra, and the manufacturer’s sizing chart.
Use the calculated result as a starting point, then check the fit of the actual bra before deciding whether the size is right for you.