Right Size Bra Calculator

Find Your Perfect Bra Size

Enter your measurements to determine your accurate bra size. For best results, measure while wearing a non-padded bra or no bra. All measurements should be snug but not tight.

Sister Size Chart

Your sister sizes are alternative sizes where the cup volume is the same. If your recommended size doesn’t fit quite right, try one of these. Go down a band size and up a cup size, or up a band size and down a cup size.

Go Down a Band Size (Tighter Band)	Your Recommended Size	Go Up a Band Size (Looser Band)
—	—	—

What is a right size bra calculator?

A right size bra calculator is an online tool designed to help you estimate your most accurate bra size based on specific body measurements. It takes the guesswork out of a notoriously tricky process. Studies suggest a vast majority of women wear the wrong bra size, leading to discomfort, poor support, and even health issues like back and neck pain. By using a right size bra calculator, you input your under-bust (band) and fullest-bust measurements, and the tool applies a standard formula to recommend a starting band and cup size. This is far more reliable than simply guessing or using outdated methods. This tool is for everyone, whether you’re buying your first bra, experiencing bodily changes, or have always felt your current bra isn’t quite right. A common misconception is that bra sizes are static, but they can change multiple times throughout your life.

Right Size Bra Calculator Formula and Mathematical Explanation

The core logic behind any effective right size bra calculator involves two key measurements. The calculation is a two-step process that determines your band size first, and then uses that result to find your cup size.

1. Step 1: Determine Band Size. You measure your ribcage just beneath your bust. This raw measurement (in inches) is then rounded to the nearest even number. This becomes your final band size. For example, a measurement of 29.5 inches or 30.2 inches would both result in a 30 band size. Some older methods, known as the “+4 method”, are now largely considered inaccurate by modern fit experts. This calculator uses the direct measurement method for better accuracy.
2. Step 2: Determine Cup Size. You measure the fullest part of your bust. The cup size is found by subtracting your final band size (from Step 1) from this fullest-bust measurement. The resulting difference in inches corresponds to a letter.

For example: If your fullest-bust is 37 inches and your calculated band size is 34, the difference is 3 inches. A 3-inch difference corresponds to a ‘C’ cup. Therefore, your estimated size is 34C. Using a right size bra calculator automates this math for you.

Variables in Bra Size Calculation

Variable	Meaning	Unit	Typical Range
Under-Bust Measurement	The circumference of the ribcage directly under the breasts.	Inches / CM	26 – 48 in
Fullest-Bust Measurement	The circumference over the most projected point of the bust.	Inches / CM	28 – 60 in
Band Size	The numbered part of the bra size, based on the under-bust.	Inches	28, 30, 32, etc.
Cup Difference	Fullest-Bust minus Band Size.	Inches	0 – 12 in
Cup Size	The letter part of the bra size, based on the Cup Difference.	Letter (A, B, C…)	AA, A, B, C, D, DD, etc.

Practical Examples (Real-World Use Cases)

Example 1: Average Measurements

• Inputs:
  • Under-Bust Measurement: 31 inches
  • Fullest-Bust Measurement: 37.5 inches
• Calculation:
  1. Band size: 31 inches rounds up to the nearest even number, which is 32.
  2. Cup difference: 37.5 inches (bust) – 32 inches (band) = 5.5 inches.
  3. Cup size: A 5.5-inch difference typically corresponds to a DD/E cup.
• Result from the right size bra calculator: 32DD or 32E.

Example 2: Smaller Band, Larger Cup

• Inputs:
  • Under-Bust Measurement: 28.5 inches
  • Fullest-Bust Measurement: 35 inches
• Calculation:
  1. Band size: 28.5 inches rounds up to the nearest even number, which is 30.
  2. Cup difference: 35 inches (bust) – 30 inches (band) = 5 inches.
  3. Cup size: A 5-inch difference corresponds to a D cup.
• Result from the right size bra calculator: 30D.

How to Use This right size bra calculator

Using this right size bra calculator is a simple process designed for accuracy and ease. Follow these steps to get your estimated size.

1. Select Your Units: Begin by choosing your preferred measurement unit, either inches or centimeters. The calculator will convert as needed.
2. Measure Your Under-Bust: Using a soft measuring tape, measure around your ribcage, just under where your breast tissue ends. The tape should be level and snug. Enter this number into the “Under-Bust Measurement” field.
3. Measure Your Fullest-Bust: Measure around the fullest part of your chest, usually over the nipples. Ensure the tape is not too tight and is parallel to the floor. Enter this value into the “Fullest-Bust Measurement” field.
4. Read Your Results: The calculator will instantly update. The primary result is your estimated bra size (e.g., 34C). You will also see the intermediate values: your calculated band size, your cup letter, and the measurement difference that determined your cup size.
5. Consider Sister Sizes: Check the Sister Size chart. If your calculated size feels off (band too tight/loose), a sister size might provide a better fit.

The goal of our right size bra calculator is to provide a reliable starting point. Always remember that brand and style variations mean you may need to adjust from this initial size. For more help, see our bra fitting guide.

Key Factors That Affect Right Size Bra Calculator Results

While a right size bra calculator provides an excellent starting point, several factors can influence your true best fit. Understanding these can help you fine-tune your size.

• Breast Shape: Are your breasts round, teardrop, slender, or asymmetrical? Different shapes sit differently in cups. A shallow shape might need a different style than a projected shape, even with the same measurements. See our breast shape guide for more info.
• Brand and Style Variation: Just like with clothing, bra sizing is not perfectly standardized across all brands. A 34C in one brand might fit differently than in another. Balconette, plunge, or full-coverage bras also have different structures.
• Time of the Month: Hormonal fluctuations can cause breast tissue to swell, changing your bust measurement slightly. It’s often best to measure mid-cycle for the most consistent result.
• Age and Life Changes: Pregnancy, weight fluctuations, and age can all dramatically change breast size and tissue density, requiring a new measurement. Using a right size bra calculator annually is a good practice.
• Band Elasticity: The material and age of a bra affect the band’s stretch. A new, firm band might feel tighter than an older, worn-in one of the same size.
• Measurement Technique: The accuracy of your result depends on how you measure. A tape that’s too loose, too tight, or not level can skew the numbers. Always double-check your measurements, which is a key step for any right size bra calculator. Our guide on how to measure bra size can help.

Frequently Asked Questions (FAQ)

1. How often should I use a right size bra calculator?

It’s recommended to measure yourself and use a right size bra calculator at least once a year, or after any significant life event like pregnancy, weight change, or starting a new hormonal medication. Your body changes, and your bra size will too.

2. What if my measurements are between sizes?

This is very common. For the band, the rule is to round to the nearest even number. For the cup, if you are between inch differences, consider your breast shape. If you have fuller tissue, sizing up the cup may be better. Trying on both potential sizes is the best approach.

3. Can I use this calculator for sports bras?

Yes, you can use the same measurements to get your starting size. However, sports bras often use S/M/L sizing and are categorized by impact level (low, medium, high). Use your calculated bra size (e.g., 36D) to find the corresponding size on the brand’s specific sports bra size chart.

4. What is a “sister size”?

Sister sizes are a group of bra sizes with the same cup volume. For example, a 34C, 32D, and 36B are sister sizes. If you go down a band size (from 34 to 32), you go up a cup size (from C to D) to maintain the volume. This is useful if your calculated band is too loose or tight.

5. Why does the “+4” method exist and why don’t you use it?

The “+4/+5” method was created decades ago when bra bands were made of non-elastic materials. Adding inches was necessary to get a comfortable fit. Modern bras use elastic, so adding extra inches often results in a band that is far too loose and unsupportive. This right size bra calculator uses the modern, more accurate “straight measurement” method.

6. My two breasts are different sizes. How should I measure?

This is completely normal. Always measure for the 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 if desired.

7. The calculator gave me a size I’ve never worn. Is it right?

It’s very possible. Since so many people wear the wrong size, getting a correct measurement from a right size bra calculator can often be surprising. The most common mistake is wearing a band that’s too big and a cup that’s too small. Trust the measurements and try on the recommended size. Look for key signs of a good fit, which are covered in our guide to common bra fit issues.

8. Does cup size scale with band size?

No, a ‘D’ cup is not the same volume across different band sizes. The cup letter is relative to the band. For instance, a 38D has a much larger total volume than a 32D, because it represents a 4-inch difference on a much larger frame.