How To Find Bra Cup Size Calculator

Find Your Bra Size

Enter your underbust (band) and fullest bust measurements to estimate your bra size.

Understanding Your Bra Size

What is a bra cup size calculator?

A bra cup size calculator is a tool designed to estimate your bra size based on two key measurements: your underbust (band) measurement and your fullest bust measurement. By inputting these measurements, the calculator determines your band size and cup size, providing you with a suggested bra size (e.g., 34C).

Anyone who wears a bra and wants to find a better fit can use a bra cup size calculator. It’s particularly useful if you’ve never been professionally fitted, have experienced body changes (like weight fluctuation or pregnancy), or feel your current bra isn’t comfortable or supportive.

Common misconceptions include thinking bra sizes are static (they can change) or that cup sizes are the same across different band sizes (a 34C is different from a 36C in volume). Another is relying solely on adding inches to the underbust for the band size, which is an older method and less accurate for many modern bras and individuals; our bra cup size calculator uses a more direct difference method for the cup and rounds the underbust for the band.

Bra Cup Size Calculator Formula and Mathematical Explanation

The calculation for bra size involves two main components:

1. Band Size: This is typically your underbust measurement, often rounded to the nearest even number in inches (e.g., if you measure 29 inches, your band size might be 30; if you measure 30, it’s 30). Some older methods added 4 or 5 inches, but many modern methods use the rounded underbust directly or with minimal addition. Our calculator rounds the underbust to the nearest even number.
2. Cup Size: This is determined by the difference between your fullest bust measurement and your calculated band size (or sometimes the raw underbust before rounding, depending on the method).
   
   Cup Difference = Bust Measurement - Band Size
   
   Each inch of difference generally corresponds to a cup letter:

Difference (inches)	US/UK Cup Letter
<1	AA
1	A
2	B
3	C
4	D
5	DD or E
6	DDD or F
7	G
8	H
9	I
10	J

Table: Cup Size based on Bust-Band Difference

The final bra size is the band size combined with the cup letter (e.g., 34C).

Variables Used in the Bra Cup Size Calculator

Variable	Meaning	Unit	Typical Range
Underbust Measurement	Measurement around the ribcage directly under the breasts	inches	26 – 50+
Bust Measurement	Measurement around the fullest part of the breasts	inches	28 – 60+
Band Size	The number part of the bra size, derived from the underbust	inches (even numbers)	28 – 52+
Cup Difference	Bust Measurement – Band Size	inches	0 – 10+
Cup Letter	The letter part of the bra size, based on Cup Difference	Letter (AA, A, B, C…)	AA – J+

Practical Examples

Let’s see how the bra cup size calculator works with real-world numbers:

Example 1:

• Underbust Measurement: 31 inches
• Bust Measurement: 36 inches
• Calculated Band Size: 32 inches (31 rounded to the nearest even number)
• Cup Difference: 36 – 32 = 4 inches
• Estimated Cup Letter: D
• Estimated Bra Size: 32D

Example 2:

• Underbust Measurement: 34 inches
• Bust Measurement: 37 inches
• Calculated Band Size: 34 inches
• Cup Difference: 37 – 34 = 3 inches
• Estimated Cup Letter: C
• Estimated Bra Size: 34C

These examples show how the measurements translate into a suggested bra size using our bra cup size calculator.

How to Use This Bra Cup Size Calculator

1. Measure Yourself: Using a soft measuring tape, measure your underbust and fullest bust in inches. For the underbust, the tape should be snug and level. For the bust, it should be level and not too tight, over the fullest part. It’s best to do this while wearing a non-padded bra or no bra.
2. Enter Measurements: Input your Underbust Measurement and Bust Measurement into the respective fields of the bra cup size calculator.
3. View Results: The calculator will instantly show your estimated Band Size, the difference between your bust and band, the corresponding Cup Letter, and your full estimated Bra Size.
4. Understand the Fit: The calculated size is a starting point. Bra fit can vary by brand and style. Consider trying sister sizes (e.g., if 34C is suggested, try 32D or 36B) if the fit isn’t quite right.

Key Factors That Affect Bra Size Results

• Measurement Accuracy: How accurately you measure yourself is crucial. A loose or tight tape can skew results from the bra cup size calculator.
• Bra Style: Different bra styles (plunge, balcony, full cup, t-shirt) fit differently even in the same size. Some may require adjusting your size.
• Brand Differences: Sizing can vary significantly between brands. You might be a 34C in one brand and a 32D in another.
• Body Changes: Weight fluctuations, hormonal changes (like pregnancy or periods), and age can all affect your breast size and shape, requiring a size re-evaluation.
• Sister Sizes: Understanding sister sizes (sizes with the same cup volume but different band and letter) can help you find a better fit if your calculated size isn’t perfect.
• Fabric and Stretch: The material and elasticity of the bra band can affect how it fits. A very stretchy band might feel looser.
• Time of Month: Breast size can fluctuate during the menstrual cycle, so measuring at different times might yield slightly different results for the bra cup size calculator.
• Rounding Method: How the band size is rounded or adjusted from the underbust measurement can vary, affecting the final size. Our calculator rounds to the nearest even number.

Frequently Asked Questions (FAQ)

What if my underbust measurement is odd?

Our bra cup size calculator rounds to the nearest even number for the band size (e.g., 29 becomes 30, 31 becomes 32). Some people prefer to go down to the nearest even for a snugger band, especially if the band fabric is stretchy.

How often should I measure myself for a bra?

It’s a good idea to remeasure every 6-12 months, or after significant body changes like weight gain/loss, pregnancy, or starting/stopping hormonal birth control.

Is the bra cup size calculator 100% accurate?

It provides a very good starting point based on standard measurements. However, due to variations in bra brands, styles, and individual body shapes, you may need to try on a few sizes around the suggested one to find the perfect fit. Consider it a guide.

What are sister sizes?

Sister sizes are bra sizes that have the same cup volume but different band lengths and cup letters. For example, 34C, 32D, and 36B are sister sizes. If your band feels too tight in a 34C, you might try a 36B. Learn more on our sister size chart page.

My two breasts are different sizes, which one do I measure?

Always fit to the larger breast to avoid compression and discomfort. You can use an insert or padding in the cup for the smaller breast if needed.

Should the measuring tape be tight or loose?

For the underbust, it should be snug but not digging in. For the bust, it should be level and just skim the body without being tight or too loose.

Does cup size change with band size?

Yes, the cup volume of a 32D is different from a 36D. The letter represents the difference relative to the band size, so a D cup on a 32 band is smaller in volume than a D cup on a 36 band.

What if the calculator gives me a size I’ve never worn?

It’s very common to be wearing the wrong bra size. Trust the measurements and the bra cup size calculator as a starting point, and be open to trying the suggested size and its sister sizes.