Find Your Bra Size Calculator

Enter your measurements to find your estimated bra size using our bra size calculator.

What is a Bra Size Calculator?

A bra size calculator is a tool designed to estimate your bra size based on your body measurements. Typically, you need two measurements: your underbust (rib cage circumference just below your breasts) and your bust (circumference around the fullest part of your breasts). The bra size calculator uses these measurements to determine your band size and cup size.

Bra sizes consist of two parts: a number (the band size, e.g., 34) and a letter or letters (the cup size, e.g., C). The band size relates to your underbust measurement, while the cup size relates to the difference between your bust and band measurements. Finding the right bra size is crucial for comfort, support, and breast health. A well-fitting bra can prevent back pain, shoulder strain, and breast discomfort.

Anyone who wears a bra can benefit from using a bra size calculator, especially if they are unsure of their current size, have experienced changes in body shape or weight, or are buying a bra from a brand they haven’t tried before. Common misconceptions include thinking bra sizes are static or that all brands size the same way. In reality, sizes can vary between brands, and your size can change over time.

Bra Size Calculator Formula and Mathematical Explanation

Our bra size calculator primarily uses the “plus 4/plus 5” method for band size calculation when inches are used, as it’s still a common reference, though we also acknowledge more modern methods. Here’s how it works:

1. Underbust Measurement: Measure snugly around your ribcage, directly under your bust. Round to the nearest whole number.
2. Band Size Calculation (Inches):
   • If your rounded underbust measurement is an even number, add 4 inches to get your band size.
   • If your rounded underbust measurement is an odd number, add 5 inches to get your band size.
   • Note: Many modern methods suggest using the rounded underbust as the band size (or rounding up to the nearest even number), especially for bands 32 and above. Fitting is personal, so consider this calculated size a starting point.
3. Bust Measurement: Measure around the fullest part of your bust, keeping the tape parallel to the floor and not too tight. Round to the nearest whole number.
4. Cup Size Calculation: Subtract your calculated band size from your rounded bust measurement. The difference in inches determines your cup size:
   • 0 inch difference = AA
   • 1 inch difference = A
   • 2 inches difference = B
   • 3 inches difference = C
   • 4 inches difference = D
   • 5 inches difference = DD (or E in some UK/EU brands)
   • 6 inches difference = DDD/F
   • 7 inches difference = G
   • And so on…
5. For CM measurements: The calculator converts cm to inches (1 cm = 0.3937 inches) and then applies the above logic.

Your bra size is the band size number followed by the cup size letter (e.g., 34C).

Variables Used

Variable	Meaning	Unit	Typical Range
Underbust Measurement	Circumference below the bust	inches or cm	24-50 inches (60-127 cm)
Bust Measurement	Circumference at the fullest part of the bust	inches or cm	28-60 inches (71-152 cm)
Band Size	The numerical part of the bra size	inches (even numbers)	28-56
Cup Difference	Bust Measurement – Band Size	inches	0-10+
Cup Size	The letter part of the bra size	Letter(s)	AA, A, B, C, D, DD, etc.

Table 1: Variables in Bra Size Calculation

Practical Examples (Real-World Use Cases)

Let’s see how the bra size calculator works with some examples:

Example 1:

• Underbust Measurement: 30 inches (rounded)
• Bust Measurement: 35 inches (rounded)
• Band Size: 30 is even, so 30 + 4 = 34
• Cup Difference: 35 – 34 = 1 inch
• Estimated Bra Size: 34A

Example 2:

• Underbust Measurement: 33 inches (rounded)
• Bust Measurement: 39 inches (rounded)
• Band Size: 33 is odd, so 33 + 5 = 38
• Cup Difference: 39 – 38 = 1 inch
• Estimated Bra Size: 38A (However, if bust was 41, difference is 3 inches -> 38C)

Example 3 (using cm):

• Underbust Measurement: 78 cm (approx 30.7 inches, rounds to 31)
• Bust Measurement: 92 cm (approx 36.2 inches, rounds to 36)
• Band Size (from 31): 31 + 5 = 36
• Cup Difference: 36 – 36 = 0 inches
• Estimated Bra Size: 36AA (using +4/+5)

It’s important to note the +4/+5 method can sometimes overestimate band size and underestimate cup size, especially for larger band or cup sizes. Many modern fitters suggest using the rounded underbust (or next even number up if odd) as the band size directly and calculating the cup from there. Our bra size calculator provides a starting point based on a common method.

How to Use This Bra Size Calculator

1. Select Units: Choose whether you are entering measurements in “Inches” or “Centimeters” using the dropdown menu.
2. Enter Underbust Measurement: Measure around your rib cage just under your bust. Enter the number into the “Underbust Measurement” field.
3. Enter Bust Measurement: Measure around the fullest part of your bust. Enter this number into the “Bust Measurement” field.
4. View Results: The calculator will automatically display your estimated band size, cup size, and full bra size. It also shows the cup difference and possible sister sizes.
5. Sister Sizes: Sister sizes are alternative bra sizes where the cup volume is the same, but the band and cup letter change (e.g., 34C has the same cup volume as 32D or 36B). If your calculated size doesn’t feel quite right, a sister size might fit better.
6. Consider the Fit: The calculated size is an estimate. Try on bras in the suggested size and sister sizes to see what feels most comfortable and supportive. Look for a snug band, no gapping or spillage in the cups, and comfortable straps.

This bra size calculator gives you a good starting point. For a more personalized fitting, consider visiting a professional bra fitter.

Key Factors That Affect Bra Size Calculator Results and Fit

Several factors influence your bra size and how a bra fits, beyond just the numbers from a bra size calculator:

• Measurement Accuracy: How snugly and level you hold the tape measure directly impacts the numbers you input into the bra size calculator.
• Brand Variations: Different manufacturers have slightly different sizing standards. A 34C in one brand might fit differently than a 34C in another.
• Bra Style: The style of the bra (e.g., balconette, full cup, plunge, sports bra) affects the shape and coverage, and thus the fit, even in the same size.
• Breast Shape and Density: Breasts come in many shapes (round, teardrop, wide-set, etc.), and their density can influence how they sit in a cup. Some shapes fit better in certain styles.
• Band Elasticity: The material and stretch of the bra band affect how snug it feels. A very stretchy band might feel looser than a firm one of the same size.
• Body Changes: Weight fluctuations, hormonal changes (like during a menstrual cycle or pregnancy), and age can all cause your bra size to change over time. Using a bra size calculator periodically is helpful.
• Rounding: How the measurements are rounded can slightly alter the calculated size.
• The +4/+5 Method: As mentioned, this method can sometimes lead to a band size that’s too large and a cup size that’s too small for some individuals, especially those with larger band sizes or smaller frames.

Frequently Asked Questions (FAQ)

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

It’s a good idea to remeasure yourself and use a bra size calculator every 6-12 months, or after significant weight changes, pregnancy, or if your current bras feel uncomfortable.

2. What if my measurements put me between sizes?

If you’re between sizes, consider trying both the smaller and larger band or cup sizes, or look at sister sizes. Fit preference (snug vs. looser band) also plays a role.

3. Are bra size calculators 100% accurate?

No bra size calculator is 100% accurate for everyone. They provide an excellent starting point based on mathematical formulas, but the best fit is determined by trying on bras and assessing comfort and support.

4. Why does the band size formula add inches to the underbust measurement?

The +4/+5 method is a traditional way to convert raw underbust measurement to band size, dating back to when bra materials were less stretchy. Modern methods often use the underbust measurement more directly or round up to the nearest even number.

5. What are sister sizes?

Sister sizes are bra sizes that have the same cup volume but different band and cup letter combinations. For example, 34C, 32D, and 36B have similar cup volumes. If a 34C band is too loose, you might try a 32D.

6. Can I use this bra size calculator for sports bras?

Sports bras often use different sizing (S, M, L, XL or based on compression levels). While the calculator gives a starting point, check the specific brand’s sports bra size chart.

7. What if my breasts are different sizes?

It’s very common for breasts to be slightly different sizes. Fit your bra to the larger breast and consider using an insert or padded cup on the smaller side if needed.

8. Does the bra size calculator work for all countries?

This calculator primarily uses logic common in US/UK sizing with the +4/+5 method. EU and other international sizing systems can differ, especially in band sizing (which often directly relates to cm underbust) and cup lettering beyond D.