Check Your Bra Size Calculator

Find your accurate bra size in seconds. This tool helps you understand your measurements to discover the perfect fit for comfort and support.

Your Sister Sizes

If your calculated size doesn’t feel quite right, you might have better luck with a “sister size.” These are sizes with the same cup volume but different band lengths. Try going down a band size and up a cup size, or vice versa.

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

This table shows alternative sizes that have the same cup volume as your calculated size.

What is a check your bra size calculator?

A check your bra size calculator is an online tool designed to estimate your correct bra size based on two key body measurements: your underbust (band) and overbust (cup). Finding the right bra size is crucial for comfort, support, and posture. Many people wear the wrong size, leading to issues like straps digging in, bands riding up, or cups gaping. This calculator uses a standard formula to give you a starting point for finding your perfect fit. Using a check your bra size calculator is the first step in solving common fit problems and improving your daily comfort.

This tool is for anyone who is unsure of their current bra size, has experienced changes in their body, or has never been professionally fitted. It demystifies the confusing world of bra sizing (e.g., what does ‘C’ cup really mean?) and empowers you to shop with more confidence.

The Bra Size Formula and Explanation

Bra sizing consists of two parts: the band size (a number, like 34) and the cup size (a letter, like C). Here’s how our check your bra size calculator determines them:

1. Band Size Formula

The band size is derived from your underbust measurement. The traditional method, which this calculator uses, ensures a snug but comfortable fit.

Band Measurement (inches) -> Rounded to nearest whole number -> If Even, Add 4. If Odd, Add 5. = Band Size

2. Cup Size Formula

The cup size represents the volume of the bust. It’s found by calculating the difference between your overbust measurement and your *calculated band size* (not your raw underbust measurement).

Overbust Measurement (inches) - Calculated Band Size (inches) = Cup Difference

This difference in inches then 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. See the full variable table below for details.

Variables used in the check your bra size calculator and their typical ranges.

Variable	Meaning	Unit	Typical Range
Underbust	The measurement around your rib cage directly under the bust.	Inches or cm	26 – 48 in
Overbust	The measurement around the fullest part of your bust.	Inches or cm	28 – 55 in
Cup Difference	The result of (Overbust – Band Size). Determines the cup letter.	Inches	1 – 10 in

Practical Examples

Example 1: A Common Size

• Inputs: Underbust = 31 inches, Overbust = 37 inches.
• Band Calculation: 31 (odd) + 5 = 36. So, the band size is 36.
• Cup Calculation: 37 (Overbust) – 36 (Band Size) = 1 inch difference. A 1-inch difference is an A cup.
• Result: 36A.

Example 2: Using Centimeters

• Inputs: Underbust = 75 cm, Overbust = 92 cm.
• Unit Conversion:
  • Underbust: 75 cm / 2.54 = 29.53 inches (rounds to 30).
  • Overbust: 92 cm / 2.54 = 36.22 inches.
• Band Calculation: 30 (even) + 4 = 34. The band size is 34.
• Cup Calculation: 36.22 (Overbust) – 34 (Band Size) = 2.22 inches difference. This rounds to a 2-inch difference, which is a B cup.
• Result: 34B.

How to Use This check your bra size calculator

1. Select Your Unit: First, choose whether you measured yourself in inches or centimeters from the dropdown menu.
2. Enter Underbust Measurement: Using a soft tape measure, measure around your ribcage just below your bust line. The tape should be level and snug. Enter this number into the “Underbust Measurement” field.
3. Enter Overbust Measurement: Measure around the fullest part of your bust. The tape should be loose enough that it doesn’t compress your chest. Enter this number into the “Overbust Measurement” field.
4. View Your Results: The calculator will automatically display your estimated bra size. It will also show you the calculated band and cup components separately. For more options, check out the sister size calculator chart that appears.
5. Interpret the Results: Your calculated size is a starting point. Different brands and styles can fit differently. Use this result to start trying on bras and see how they feel.

Key Factors That Affect Bra Size

Your bra size isn’t static. Several factors can influence the fit and size you need. A good check your bra size calculator gives you a baseline, but consider these factors:

• Brand Differences: Sizing can vary significantly from one brand to another. A 34C in one brand might fit like a 34D in another.
• Bra Style: A plunge bra, a t-shirt bra, and a full-cup bra will all fit differently due to their construction. Our guide on bra styles explained can help.
• Time of the Month: Hormonal fluctuations can cause breast size to change throughout your menstrual cycle.
• Weight Changes: Gaining or losing weight will almost certainly affect your band and cup size. It’s a good idea to remeasure every 6-12 months.
• Breast Shape: Shape (e.g., round, slender, teardrop) can affect how you fill out a cup, even if your volume measurement is correct. Some styles work better for certain shapes. This is a key part of our bra fitting guide.
• Age and Pregnancy: Life events like pregnancy, breastfeeding, and menopause dramatically alter breast tissue and size.

Frequently Asked Questions (FAQ)

• Q: How often should I check my bra size?
  A: It’s a good practice to use a check your bra size calculator and remeasure yourself every 6 to 12 months, or after any significant life event like weight change or pregnancy.
• Q: My measurement was between numbers. What should I do?
  A: For the underbust, round to the nearest whole number. For the overbust, it’s generally better to round up if you are between half-inches.
• Q: The calculator gave me a size I’ve never worn before. Is it right?
  A: It could be! An estimated 80% of people wear the wrong bra size. The most common mistake is wearing a band that’s too big and a cup that’s too small. Give your new size a try, along with its sister sizes. A detailed bra size chart can also be helpful.
• Q: What is a “sister size”?
  A: Sister sizes are alternate sizes where the cup volume is the same. For example, a 34C has the same cup volume as a 32D and a 36B. If your band feels too tight in a 34C, you could try a 36B.
• Q: Why does this calculator add 4 or 5 inches to my underbust?
  A: This is the traditional “plus-four” method of bra fitting, which accounts for the stretch in older elastic materials. While some modern methods don’t add inches, this system is still widely used by many major brands and provides a reliable starting point.
• Q: Does cup size mean the same thing on different band sizes?
  A: No. A ‘C’ cup on a 32 band is smaller in volume than a ‘C’ cup on a 38 band. The letter is relative to the band size. This is one of the biggest common fit issues people encounter.
• Q: Can I measure myself over a shirt?
  A: No, for the most accurate results, you should measure yourself while wearing no bra or a thin, non-padded bra. Our how to measure bra size guide has visuals.
• Q: Is this calculator accurate for all countries?
  A: This calculator uses the US/UK sizing system. Sizing can differ in European (EU) or French (FR) systems.