Bra Size Calculator
Finding the right bra size can be surprisingly difficult. Measurements are often taken differently, sizing systems vary by country, and the same labeled size can fit differently depending on the brand and bra style. A Bra Size Calculator can simplify the process by turning two basic body measurements into an estimated bra size.
This calculator uses your band measurement and bust measurement to estimate your band size and cup size. It supports four regional options: United States, United Kingdom, Europe, and Australia. The calculator also shows the difference between your bust and band measurements and provides two potential sister sizes.
Whether you are shopping for a new bra, comparing international sizing, or checking whether your current size is close to an appropriate measurement-based size, this calculator provides a convenient starting point.
What Is a Bra Size Calculator?
A bra size calculator is a tool that estimates bra size from measurements taken around the torso and bust.
The two measurements used by this calculator are:
- Band Measurement: The measurement taken snugly underneath the bust.
- Bust Measurement: The measurement taken around the fullest part of the bust.
The difference between these measurements is used to estimate the cup size, while the band measurement is processed according to the selected regional sizing system.
The calculator provides five results:
- Your Bra Size
- Band Size
- Cup Size
- Bust-Band Difference
- Sister Sizes
The calculator supports:
- United States
- United Kingdom
- Europe
- Australia
Because actual bra sizing can vary between manufacturers, these results are best used as an estimate and starting point.
How to Use the Bra Size Calculator
Using the calculator only requires two measurements.
Step 1: Measure Your Band
Wrap a flexible measuring tape around your torso directly underneath your bust.
The tape should be snug without being uncomfortably tight. Try to keep it level around your body.
Enter the measurement in inches.
For example:
Band measurement: 34 inches
Step 2: Measure Your Bust
Next, measure around the fullest part of your bust. Keep the tape level and avoid pulling it tightly enough to compress the bust.
For example:
Bust measurement: 38 inches
Step 3: Select Your Region
Choose the sizing system that corresponds to the region you want to use:
- United States
- United Kingdom
- Europe
- Australia
This selection affects how the band size is calculated.
Step 4: Click Calculate
Select the Calculate button.
The calculator will display your estimated bra size, band size, cup size, bust-band difference, and sister sizes.
If the measurements are missing, invalid, or the bust measurement is smaller than the band measurement, you will be asked to correct the information.
How the Bra Size Calculation Works
The calculator begins by finding the difference between the bust and band measurements.
The basic formula is:
Bust Measurement − Band Measurement = Bust-Band Difference
For example, if your band measurement is 34 inches and your bust measurement is 38 inches:
38 − 34 = 4 inches
The calculator then rounds this difference to determine the position within its cup-size scale.
The cup-size sequence used by the calculator is:
AA, A, B, C, D, DD, E, F, FF, G, GG, H, HH, J, JJ, K
The resulting cup index is limited to this range, so measurements outside the available range are assigned to the nearest available cup category.
How Band Size Is Calculated
The band calculation depends on your selected region.
United States
For the United States option, the calculator first rounds the band measurement to the nearest whole number. If the resulting number is odd, it increases it by one to create an even number.
Four inches are then added.
For example:
34 inches → 34 + 4 = 38
The estimated band size is therefore:
38
United Kingdom
The calculator uses the same numerical band calculation for the United Kingdom option.
For example:
34-inch band measurement → 38 band
The cup-size sequence used by the calculator includes UK-style double-letter categories such as FF, GG, HH, and JJ.
However, actual UK brands can have their own size charts, so it is important to check the individual manufacturer’s conversion information when buying a specific product.
Europe
European sizing is handled differently. The calculator converts the inch measurement to centimeters and rounds it to the nearest five centimeters.
The conversion uses:
1 inch = 2.54 centimeters
For example, with a 34-inch band measurement:
34 × 2.54 = 86.36 cm
The result is rounded to the nearest 5 cm:
85
The estimated European band size is therefore 85.
Australia
The calculator uses the same numerical band calculation as the US and UK options for the Australian selection.
The final cup category is then combined with the calculated band size.
Australian manufacturers can use their own size conventions, so brand-specific charts remain important when purchasing a bra.
Worked Example: 34-Inch Band and 38-Inch Bust
Suppose you enter:
- Band measurement: 34 inches
- Bust measurement: 38 inches
- Region: United States
First, calculate the difference:
38 − 34 = 4 inches
The calculator rounds the difference to 4.
The cup-size list starts with:
- 0 = AA
- 1 = A
- 2 = B
- 3 = C
- 4 = D
Therefore, the estimated cup size is:
D
The US band calculation is:
34 + 4 = 38
The estimated result is:
38D
The calculator would also show:
- Band Size: 38
- Cup Size: D
- Bust-Band Difference: 4.0 inches
It would then generate two sister-size alternatives.
Understanding the Bust-Band Difference
The Bust-Band Difference is one of the most important values in the calculation.
It represents the numerical difference between your bust measurement and your band measurement.
For example:
| Band | Bust | Difference |
|---|---|---|
| 32 inches | 35 inches | 3 inches |
| 34 inches | 38 inches | 4 inches |
| 36 inches | 41 inches | 5 inches |
| 38 inches | 44 inches | 6 inches |
The calculator uses this difference to select the cup category.
A larger difference moves further along the calculator’s cup-size sequence, while a smaller difference corresponds to an earlier cup category.
However, this should not be interpreted as a universal bra-sizing rule. Different sizing systems and manufacturers use different methods.
Understanding Your Cup Size
The cup size is represented by a letter or combination of letters.
This calculator uses:
AA, A, B, C, D, DD, E, F, FF, G, GG, H, HH, J, JJ, K
For example, a result of 36F means:
- 36 = estimated band size
- F = estimated cup category
It is important to remember that cup letters do not represent an absolute volume on their own. Cup volume is related to the band size.
This is why sister sizes can be useful when comparing different band measurements.
What Are Sister Sizes?
Sister sizes are alternative bra sizes that use different band sizes while adjusting the cup size in the opposite direction.
The goal is to maintain a relatively similar cup volume.
For non-European sizing in this calculator, the band changes by 2 inches. The cup category changes in the opposite direction.
For European sizing, the band changes by 5 centimeters.
For example, if the calculator produces a particular size, one sister size uses a smaller band with the next cup category, while another uses a larger band with the previous cup category.
Sister sizes can be useful when:
- Your usual band feels too tight.
- Your usual band feels too loose.
- Your preferred size is unavailable.
- You want to compare alternative sizes from a particular retailer.
Sister sizes are not guaranteed to fit identically, however. Changing the band can change how the bra sits on your body.
Why Sister Sizes Matter
Imagine that a bra’s cups seem to fit well but the band feels too tight.
Simply choosing a smaller band number is not necessarily the right solution because the cup volume also changes. A sister-size approach accounts for both measurements.
Likewise, if the band feels too loose, a smaller band combined with a larger cup category may provide a closer alternative.
This makes sister sizes especially useful when shopping online or when a preferred size is unavailable.
Comparing US, UK, EU, and Australian Sizing
International bra sizing can be confusing because regional systems are not interchangeable.
US Sizing
The calculator produces an even-numbered band after processing the underbust measurement and adding four inches.
UK Sizing
The calculator uses the same numerical band calculation as its US option and includes double-letter cup categories such as FF, GG, HH, and JJ.
EU Sizing
European sizing uses centimeters. The calculator converts the inch measurement to centimeters and rounds it to the nearest five.
Australian Sizing
The calculator uses the same numerical band calculation as the US and UK selections, while applying the calculator’s cup-size sequence.
Because individual brands can differ, the regional setting should be considered an estimate rather than a universal conversion table.
How to Measure Yourself Accurately
Accurate measurements are essential for getting a useful calculator result.
Use a Flexible Measuring Tape
A soft tape designed for body measurements is ideal. It can follow the natural shape of your torso without creating gaps.
Measure Under the Bust Snugly
For the band measurement, place the tape directly underneath your bust and keep it snug.
Do not intentionally pull the tape excessively tight.
Measure Around the Fullest Part
For the bust measurement, position the tape around the fullest part of your bust.
Keep the tape approximately horizontal around your body.
Avoid Thick Clothing
Heavy clothing can add to the measurement and affect the result. Whenever possible, measure over minimal clothing or clothing that does not add significant bulk.
Repeat Your Measurements
If you are unsure of a measurement, take it again. Consistent measurements are more useful than relying on a single uncertain reading.
Why Your Calculator Size May Differ From Your Current Bra
It is normal for a calculator to produce a different size from the label on a bra you already own.
There are several possible explanations.
Different brands use different sizing standards. A size from one manufacturer may not fit exactly like the same labeled size from another.
Bra styles affect fit. Sports bras, molded cups, wireless bras, balconette styles, plunge bras, and other designs can fit differently.
Sizing systems differ internationally. A US, UK, EU, and Australian label may use different conventions.
Measurements may differ. Small changes in tape position or tension can alter the calculated result.
Body shape matters. Two people can have the same measurements but different breast shapes, distributions, or asymmetry.
Consequently, a calculator should be viewed as a starting point rather than a definitive answer for every bra.
Tips for Using Your Calculated Bra Size
Once you have your estimated size, compare it with the manufacturer’s size chart before purchasing.
When shopping online, check whether the product uses:
- US sizing
- UK sizing
- EU sizing
- Australian sizing
Also check whether the retailer provides a conversion chart.
If your calculated size is unavailable, look at the sister sizes provided by the calculator. These may give you additional options to investigate.
Customer reviews can also provide useful information about whether a particular bra tends to fit differently from its labeled size.
Common Bra-Fitting Considerations
The number and letter on the label are only part of the fitting process.
A bra should generally feel secure without causing significant discomfort. The band should provide support without feeling painfully restrictive.
The cups should also accommodate the bust appropriately. Gaping, excessive compression, or visible overflow can indicate that the size or style may not be suitable.
Strap positioning and adjustment also matter. A poorly adjusted strap can create discomfort even when the underlying size is appropriate.
Underwire shape can also influence comfort and fit. Two bras in the same labeled size can feel quite different because their underwires and cup shapes are constructed differently.
Limitations of This Bra Size Calculator
This calculator provides an estimate based on two measurements and a predefined sizing system.
It does not account for every factor that affects real-world bra fit, including:
- Breast shape
- Breast asymmetry
- Underwire dimensions
- Cup shape
- Bra construction
- Fabric stretch
- Strap placement
- Brand-specific sizing
- Individual comfort preferences
The calculator also uses a fixed cup-size sequence. Actual manufacturers may offer different cup labels, additional sizes, or different conversion systems.
For the most reliable shopping decision, compare the calculated result with the specific brand’s size chart and consider how the actual garment fits.
Frequently Asked Questions
1. What measurements does the Bra Size Calculator need?
It needs your band measurement taken underneath the bust and your bust measurement taken around the fullest part.
2. Should both measurements be entered in inches?
Yes. The calculator’s input fields are designed for measurements in inches.
3. What is the bust-band difference?
It is the bust measurement minus the band measurement. The calculator uses this difference to select the estimated cup category.
4. Why does the calculator require the bust measurement to be larger?
The calculation assumes that the measurement around the fullest part of the bust is at least as large as the measurement underneath the bust.
5. Does the calculator support US bra sizes?
Yes. United States is one of the available regional options.
6. Does it calculate UK bra sizes?
Yes. The calculator includes a United Kingdom option and uses a cup sequence containing double-letter categories such as FF, GG, HH, and JJ.
7. Can I calculate an EU bra size?
Yes. Selecting Europe converts the underbust measurement from inches to centimeters and rounds it to the nearest five-centimeter band size.
8. Does the calculator support Australian sizing?
Yes. Australia is one of the four available regional selections.
9. Why can the same measurements produce different regional sizes?
Different countries use different bra-sizing conventions. Band numbers and cup labels are not universally standardized across markets.
10. What are sister sizes?
Sister sizes are alternative bra sizes that change the band measurement while adjusting the cup category to maintain a similar overall cup volume.
11. Why would I use a sister size?
A sister size can be useful if your calculated size is unavailable or if the band feels too tight or too loose while the cup fit is close.
12. Is a calculated bra size guaranteed to fit?
No. The result is an estimate based on measurements and the calculator’s formula. Brand, style, construction, and body shape can all affect fit.
13. Why does my existing bra have a different size?
Your existing bra may come from a different brand or sizing system, or its particular style may fit differently. Your measurements may also have changed.
14. Should I check the manufacturer’s size chart?
Yes. The calculator provides a useful starting estimate, but a manufacturer’s own size chart is important when purchasing a specific bra.
15. How can I improve the accuracy of my result?
Use a flexible measuring tape, measure the band snugly underneath the bust, measure around the fullest part of the bust, keep the tape level, and repeat the measurements if necessary.
Final Thoughts
The Bra Size Calculator provides a convenient way to estimate your bra size from two simple measurements. By entering your band and bust measurements, you can calculate an estimated band size, cup size, bust-band difference, and two sister-size options.
The calculator also makes it easier to compare regional sizing by providing options for the United States, United Kingdom, Europe, and Australia.
For the best results, take your measurements carefully and make sure you select the appropriate regional system. When shopping, use the calculated size as a starting point and compare it with the individual manufacturer’s sizing chart.
Bra fit depends on more than measurements alone. Different brands, styles, materials, cup shapes, and body proportions can all influence comfort and fit. Using measurements together with brand-specific information gives you a more practical approach to finding a bra that works for you.