Bra Cup Size Calculator
Determine your correct bra cup size using your underbust and bust measurements. Our calculator uses standard sizing methods to help you find a comfortable, well-fitting bra.
Your Measurements
Bust - Underbust Difference: 0 in
Best Bra for You:
Understanding Bra Cup Size Calculation
Finding the right bra size is essential for comfort, support, and overall well-being. A well-fitting bra can improve posture, reduce back and shoulder pain, and help you feel more confident. Our bra cup size calculator uses standard sizing methods to help you determine your correct size based on two simple measurements: your underbust and bust circumference.
What is Bra Cup Size?
Bra cup size is a measure of the volume of your breasts relative to your band size. It is calculated by subtracting your underbust measurement (the band size) from your bust measurement (the fullest part of your chest). The difference in inches corresponds to a specific cup letter. For example, a 1-inch difference typically corresponds to an A cup, a 2-inch difference to a B cup, and so on.
Key Factors Affecting Bra Size Calculation
| Factor | Description | Impact on Sizing |
|---|---|---|
| Underbust Measurement | Circumference around your ribcage, directly under your bust | Determines band size (e.g., 32, 34, 36) |
| Bust Measurement | Circumference around the fullest part of your bust | Used with underbust to calculate cup size |
| Difference (Bust - Underbust) | The numerical difference between the two measurements | Directly determines cup letter (A, B, C, etc.) |
| Measurement Unit | Inches or centimeters | Must be consistent for accurate calculation |
| Body Shape & Breast Shape | Individual variations in breast tissue distribution | May require sister size adjustments for comfort |
How to Take Accurate Measurements
- Wear a Comfortable, Unpadded Bra: This provides a natural shape and prevents padding from skewing measurements.
- Use a Soft Measuring Tape: Ensure the tape is not twisted and lies flat against your skin.
- Underbust Measurement: Wrap the tape snugly around your ribcage, directly under your bust. Ensure it is level all the way around. Exhale naturally before reading the measurement.
- Bust Measurement: Wrap the tape around the fullest part of your bust, usually at nipple level. Keep the tape parallel to the floor and not too tight. Stand straight and relax your arms at your sides.
- Double-Check: Take each measurement twice to ensure consistency.
Understanding Cup Size Letters
Standard Cup Size Chart
The cup size is determined by the difference between bust and underbust measurements. Here's a general guide (for inches):
- 0-1 inch difference: AA or A cup
- 1-2 inches: A or B cup
- 2-3 inches: B or C cup
- 3-4 inches: C or D cup
- 4-5 inches: D or DD (E) cup
- 5-6 inches: DD/E or F cup
- 6-7 inches: F or G cup
- 7-8 inches: G or H cup
- 8-9 inches: H or I cup
- 9-10 inches: I or J cup
Note: Cup sizes are not standardized across all brands and countries. This calculator uses a common US/UK sizing convention. Always refer to the specific brand's size chart when shopping.
Band Size
Your band size is typically your underbust measurement rounded to the nearest even number. For example, if your underbust is 31 inches, your band size is likely 32. If it's 33 inches, your band size might be 34. Some brands use odd numbers or different rounding rules.
Sister Sizes
If your calculated size isn't available or comfortable, you can try a "sister size." This involves going up a band size and down a cup size (or vice versa) while maintaining a similar cup volume. For example, a 34C is a sister size to a 32D and a 36B.
Common Bra Sizing Scenarios
| Underbust (in) | Bust (in) | Difference | Approx. Size |
|---|---|---|---|
| 30 | 31 | 1 | 30A |
| 32 | 35 | 3 | 32C |
| 34 | 38 | 4 | 34D |
| 36 | 42 | 6 | 36E (DD) |
| 38 | 45 | 7 | 38F |
| 40 | 48 | 8 | 40G |
Frequently Asked Questions
General Bra Sizing Questions
How accurate is the bra cup size calculator?
Our calculator provides a reliable estimate based on standard sizing formulas. However, actual fit can vary due to brand differences, body shape, and breast shape. It is always recommended to try on bras in your calculated size and adjust as needed. Use our result as a starting point for your fitting journey.
Why does my calculated size differ from what I usually wear?
Several factors can cause discrepancies:
- Many people wear the wrong size without realizing it.
- Brands have different sizing standards (vanity sizing).
- Weight fluctuations, hormonal changes, and aging can alter breast size.
- Measurement errors can occur if the tape is not level or properly positioned.
What is the ideal bra fit?
A well-fitting bra should:
- The band should be snug and level around your ribcage, providing most of the support.
- The center gore (the piece between the cups) should lie flat against your sternum.
- The cups should fully contain your breasts without spilling or gaping.
- The straps should be comfortable and not dig into your shoulders.
- The underwire should sit flat against your ribcage, not on breast tissue.
Measurement and Sizing Questions
How do I measure my underbust correctly?
To measure your underbust:
- Stand in front of a mirror to ensure the tape is level.
- Wrap a soft measuring tape snugly around your ribcage, directly under your bust.
- Ensure the tape is parallel to the floor and not twisted.
- Exhale naturally and read the measurement in inches.
How do I measure my bust correctly?
To measure your bust:
- Wrap the tape around the fullest part of your bust, usually at nipple level.
- Keep the tape parallel to the floor.
- Ensure the tape is not too tight or too loose; it should lie flat against your skin.
- Stand straight and relax your arms at your sides.
What if my underbust measurement is an odd number?
Bra band sizes typically come in even numbers (e.g., 32, 34, 36). If your underbust measures an odd number, you can either round down to the nearest even number for a snugger fit or round up for a looser fit. Our calculator will use the nearest even band size for the final result.
Technical and Fit Questions
What is the difference between US and UK bra sizes?
US and UK bra sizes are similar but not identical. The main difference lies in cup size progression:
- US sizing includes DD, DDD, and sometimes DDDD (or F).
- UK sizing includes DD, E, F, FF, G, etc.
- Band sizes are generally the same in inches.
- Always check the brand's specific size chart if you're shopping internationally.
How do I know if my bra band is too tight or too loose?
Signs of an incorrect band size:
- Too tight: The band rides up your back, causes red marks, or makes it difficult to breathe.
- Too loose: The band slides down when you raise your arms, or the back rides up.
- Correct fit: The band stays in place, feels snug but comfortable, and you can fit two fingers under the band.
What are sister sizes and should I use them?
Sister sizes are alternate sizes that have the same cup volume but different band sizes. For example, if you wear a 34C, your sister sizes are 32D and 36B. They can be useful if a particular size is unavailable or if you need a slightly different band fit. However, they may not always provide the perfect fit, so use them as a fallback.
Maintenance and Troubleshooting Questions
How often should I re-measure my bra size?
It's a good idea to re-measure every 6-12 months or after significant body changes such as weight loss/gain, pregnancy, or hormonal shifts. Your size can also change with age.
Why does my bra fit differently at different times of the month?
Hormonal fluctuations can cause breast size to change by up to a cup size during your menstrual cycle. It's normal to have bras in slightly different sizes for different times of the month.
What if the calculator gives me a size that doesn't feel right?
If the calculated size doesn't feel comfortable, consider:
- Re-measuring to ensure accuracy.
- Trying sister sizes.
- Visiting a professional bra fitter for a personalized fitting.
- Different brands may fit differently, so don't be afraid to try multiple sizes.
Usage and Best Practices Questions
Should I measure over or under my clothes?
For the most accurate measurement, measure over a thin, unpadded bra or bare skin. Measuring over thick clothing can add extra inches and result in an incorrect size.
Can I use this calculator for sports bras?
This calculator is designed for standard bras. Sports bras often use a different sizing system (S, M, L) and are meant to provide a different type of support. Use your calculated size as a reference but refer to the sports bra brand's specific sizing guide.
How can I make my bras last longer?
To extend the life of your bras:
- Hand wash or use a lingerie bag on a gentle cycle.
- Air dry rather than tumble dry.
- Rotate your bras to avoid overstretching a single one.
- Store them properly to maintain shape.