Bra Size Calculator
Find your perfect fit accurately and instantly. Over 80% of women wear the wrong bra size; let’s fix that!
Please enter a valid, positive number.
Please enter a valid, positive number.
Measurement Visualization
Visual comparison of your underbust and bust measurements.
Sister Size Chart
If your recommended size doesn’t feel right, a sister size might be a better fit. These sizes have the same cup volume.
| Go Down a Band Size (Go Up a Cup Size) |
Your Calculated Size | Go Up a Band Size (Go Down a Cup Size) |
|---|---|---|
| — | — | — |
What is a Bra Size Calculator?
A Bra Size Calculator is an essential tool designed to help you determine your most accurate bra size based on specific body measurements. Since studies show that a vast majority of women—up to 80%—are wearing an incorrectly sized bra, using a calculator is the first step toward better comfort, support, and health. It takes the guesswork out of bra shopping by providing a reliable starting point based on your unique proportions. A good Bra Size Calculator considers both your underbust (band) and full bust measurements to recommend a band size (the number) and a cup size (the letter).
Who Should Use It?
Every person who wears a bra should use a Bra Size Calculator periodically. Your body changes over time due to factors like weight fluctuations, hormonal shifts, pregnancy, and aging. Therefore, the size that fit you perfectly a year ago may not be your best fit today. It is especially crucial for those experiencing discomfort like digging straps, a riding-up band, or gaping cups. Finding the right fit with a Bra Size Calculator can alleviate posture problems, back pain, and skin irritation.
Common Misconceptions
One of the biggest misconceptions is that cup size is static; for example, that a ‘C’ cup is the same across all band sizes. In reality, cup volume is relative to the band size. A 32C has a smaller cup volume than a 36C. Another myth is that you should add 4 or 5 inches to your underbust measurement—an outdated method that often leads to a band that is too loose. A modern Bra Size Calculator uses a more direct and accurate measurement system.
Bra Size Calculator Formula and Mathematical Explanation
The logic behind a modern Bra Size Calculator is straightforward and involves two primary calculations: determining the band size and then the cup size.
1. Band Size Calculation: The band size is derived from the underbust measurement. You measure snugly around your ribcage, directly underneath your breast tissue. This raw measurement is then typically rounded to the nearest even number. This ensures the band is snug enough to provide the majority of the bra’s support (about 80% of it).
2. Cup Size Calculation: The cup size is found by subtracting your final band size from your full bust measurement (taken around the widest part of your chest). The resulting difference in inches corresponds to a letter. For example, a 1-inch difference is an ‘A’ cup, a 2-inch difference is a ‘B’ cup, and so on.
Bra Size = [Rounded Band Measurement] + [Cup Letter from (Bust - Band) Difference]
Variables Table
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Underbust Measurement | The measurement around the ribcage directly under the breasts. | in / cm | 26 – 48 in |
| Bust Measurement | The measurement around the fullest part of the bust. | in / cm | 28 – 55 in |
| Band Size | The underbust measurement rounded to the nearest even number. | Numeric (e.g., 32, 34) | 28 – 50 |
| Cup Difference | Bust Measurement minus Band Size. | inches | 0 – 12 in |
| Cup Size | The letter corresponding to the Cup Difference. | Letter (A, B, C…) | AA – K |
Practical Examples (Real-World Use Cases)
Example 1: Smaller Frame
Let’s say a person measures themselves and gets the following numbers:
- Underbust Measurement: 29.5 inches
- Bust Measurement: 34 inches
Using our Bra Size Calculator, the process is:
- Calculate Band Size: The underbust of 29.5 inches is rounded up to the nearest even number, which is 30.
- Calculate Cup Size: Subtract the band size from the bust measurement: 34″ – 30″ = 4″ difference.
- Determine Cup Letter: A 4-inch difference corresponds to a D cup.
Result: The calculated bra size is 30D. This is a perfect example of why you can’t just guess; many would not assume these measurements lead to a D cup.
Example 2: Fuller Frame
Another person provides the following measurements:
- Underbust Measurement: 37 inches
- Bust Measurement: 43 inches
The Bra Size Calculator would work as follows:
- Calculate Band Size: The underbust of 37 inches is rounded up to the nearest even number, 38.
- Calculate Cup Size: Subtract the new band size from the bust measurement: 43″ – 38″ = 5″ difference.
- Determine Cup Letter: A 5-inch difference corresponds to an E cup (often labeled as DD in the US).
Result: The starting bra size is 38E (DD). This demonstrates how the Bra Size Calculator adapts to all body types.
How to Use This Bra Size Calculator
Using our Bra Size Calculator is simple and fast. Follow these steps for an accurate result:
- Select Your Units: First, choose whether you are measuring in inches or centimeters from the dropdown menu.
- Measure Your Underbust: For an accurate band measurement, wrap a soft measuring tape snugly around your ribcage, just beneath your breasts. Ensure the tape is parallel to the floor and exhale fully to get the smallest measurement. Enter this number into the “Underbust Measurement” field.
- Measure Your Bust: Next, measure around the fullest part of your chest. The tape should be level and not too tight—it should just skim the body without compressing breast tissue. Enter this number into the “Bust Measurement” field.
- Read Your Results: The calculator will instantly display your calculated bra size in the highlighted green box. It also provides your key intermediate values, like the exact band and cup difference used in the calculation.
- Consult the Sister Size Chart: The table below the calculator shows your sister sizes. If your calculated size feels off (e.g., the band is a bit loose), a sister size may provide a better fit.
Key Factors That Affect Bra Size Results
Your bra size isn’t static. Several factors can influence your measurements and how a bra fits. A good Bra Size Calculator provides a starting point, but understanding these variables is key to finding true comfort.
- Brand Inconsistencies: There is no universal standard for bra sizing. A 34C from one brand can fit very differently from a 34C in another. Always be prepared to try a size up or down.
- Bra Style: The type of bra—plunge, balconette, full-cup, t-shirt bra—dramatically affects fit. A molded t-shirt bra may reveal gaping if your breast shape isn’t a match, while a stretch-lace balconette can be more forgiving. See our breast shape guide to learn more.
- Weight Changes: Gaining or losing even 5-10 pounds can alter both your band and cup size. Since breast tissue is partly composed of fat, it’s one of the first places you might notice a change. Re-measure with a Bra Size Calculator after any significant weight fluctuation.
- Hormonal Fluctuations: Your menstrual cycle, pregnancy, and menopause can cause your breasts to swell and feel more tender, temporarily changing your cup size. It’s not uncommon to need a slightly larger, more comfortable bra during certain times of the month.
- Age and Elasticity: Over time, skin and breast tissue lose elasticity. This can change the shape and position of your breasts, meaning the bra style that worked for you in your twenties might not offer the right support in your forties.
- Measurement Accuracy: How you measure matters. A tape that’s too tight or too loose, or not held level, can skew your results. For the best outcome from a Bra Size Calculator, ensure your measurements are as precise as possible. A proper bra fitting guide is invaluable.
Frequently Asked Questions (FAQ)
A sister size is a bra size with the equivalent cup volume to another size. For example, a 34C has the same cup volume as a 32D and a 36B. If a bra’s band feels too tight but the cups fit well, you can try going up one band size and down one cup size (e.g., from 34C to 36B). Our Bra Size Calculator provides your closest sister sizes.
A well-fitting bra has a snug, level band that provides most of the support. The cups should fully contain your breast tissue with no spilling or gaping. The center panel (gore) should lie flat against your sternum. Straps should not dig in or fall off. If you have these issues, consulting a how a bra should fit guide can help.
This is where sister sizing is useful. If the Bra Size Calculator puts you between, say, a 32D and 34C, consider the fit issues. If bands usually feel tight, try the 34C. If you prefer a snugger band for more support, try the 32D. It also depends on the brand and style of the bra.
Most women wear bras with bands that are too large and cups that are too small. Society often has a skewed perception of cup sizes (e.g., thinking a ‘D’ cup is huge). A Bra Size Calculator uses precise math, often revealing that a smaller, more supportive band requires a larger cup letter to contain all the breast tissue properly.
It’s a good practice to measure yourself and use a Bra Size Calculator at least once a year, or after any significant life changes like pregnancy, starting a new workout regimen, or gaining/losing more than 10 pounds.
Absolutely. Your breast shape (e.g., shallow, projected, east-west, bell-shaped) affects which bra styles will fit you best, even if the size is technically correct. A Bra Size Calculator gives you the size, but a breast shape guide helps you choose the right bra type.
This Bra Size Calculator provides your standard lingerie bra size. Sports bras often use different sizing (like S, M, L) based on compression needs. However, knowing your accurate bra size is an excellent starting point for finding your corresponding size in most sports bra brands.
This is extremely common. Always fit your larger breast to avoid uncomfortable compression. You can then use a small insert or “cookie” in the cup for the smaller breast to create a symmetrical look, or choose bras with stretch lace cups that can accommodate slight differences.