Check Your Bra Size Calculator

Find your perfect fit in under a minute! Measure your underbust and bust, enter the values below, and our bra size calculator will determine your accurate size. For best results, use a soft measuring tape and measure while wearing a non-padded bra.

Your Estimated Bra Size

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Formula Used:

1. Band Size: Your underbust measurement is rounded to the nearest even number. This forms the numerical part of your bra size.
2. Cup Size: The difference between your bust and your calculated band size determines your cup letter (1″ difference = A, 2″ = B, etc.).

Sister Size Chart

If a bra in your calculated size doesn’t feel right, you might have better luck with a “sister size.” These sizes have the same cup volume. If you go down a band size, go up a cup size, and vice versa.

Band Down, Cup Up	Your Size	Band Up, Cup Down
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Sister sizes for your calculated bra size.

What is a Bra Size Calculator?

A bra size calculator is an online tool designed to estimate a person’s correct bra size based on body measurements. The primary goal is to solve a widespread problem: studies suggest that a vast majority of women wear incorrectly fitted bras, leading to discomfort, poor support, and negative effects on posture and confidence. This tool takes the guesswork out of the process by using a standardized measurement system.

Anyone who wears a bra should consider using a bra size calculator, especially if they experience common fit issues like slipping straps, a riding-up band, cup spillage, or painful underwires. It’s also invaluable when purchasing bras online, where you can’t try them on first. A common misconception is that bra sizes are consistent across all brands; however, they can vary significantly. Using a bra size calculator gives you a reliable starting point to find your best fit in any brand.

Bra Size Calculator Formula and Mathematical Explanation

The calculation for bra size is a two-step process that determines your band size and cup size. While there are different methods, the most common one used by our bra size calculator is as follows:

1. Step 1: Determine Band Size. The band is the foundation of the bra’s support. It’s determined by measuring the circumference of the ribcage directly under the bust. This raw measurement (in inches) is then rounded to the nearest even number. For example, if you measure 31 inches, your band size is 32. If you measure 32.5 inches, your band size would be 32, but you might also try a 34.
2. Step 2: Determine Cup Size. The cup size represents the volume of the breasts. It’s found by subtracting the calculated band size from the bust measurement (taken at the fullest point). The resulting difference in inches corresponds to a letter.

Variable Explanations

Variable	Meaning	Unit	Typical Range
Underbust Measurement	The measurement around the ribcage directly under the bust.	inches	26 – 48
Bust Measurement	The measurement around the fullest part of the bust.	inches	28 – 60
Band Size	The numerical part of the bra size, derived from the underbust.	N/A	28 – 50 (even numbers)
Cup Size (Difference)	Bust Measurement – Band Size. This difference maps to a letter.	inches	1 (A), 2 (B), 3 (C), etc.

Practical Examples (Real-World Use Cases)

Example 1: Average Measurements

• Inputs:
  • Underbust Measurement: 31.5 inches
  • Bust Measurement: 37 inches
• Calculation:
  1. Band Size: 31.5 inches rounds up to the nearest even number, which is 32.
  2. Cup Difference: 37 inches (Bust) – 32 inches (Band) = 5 inches.
  3. Cup Size: A 5-inch difference corresponds to a DD cup.
• Result: The estimated size from the bra size calculator is 32DD.

Example 2: Smaller Band, Larger Cup

• Inputs:
  • Underbust Measurement: 28 inches
  • Bust Measurement: 34 inches
• Calculation:
  1. Band Size: 28 inches is already an even number, so the band size is 28.
  2. Cup Difference: 34 inches (Bust) – 28 inches (Band) = 6 inches.
  3. Cup Size: A 6-inch difference corresponds to an F cup (in US sizing).
• Result: The estimated size from the bra size calculator is 28F.

How to Use This Bra Size Calculator

Using our bra size calculator is simple and fast. Follow these steps to get your personalized result:

1. Enter Your Underbust Measurement: Using a soft measuring tape, measure around your ribcage right where a bra band would sit. Ensure the tape is snug and level. Enter this number in the “Underbust Measurement” field.
2. Enter Your Bust Measurement: Measure loosely around the fullest part of your chest, typically across the nipples. Make sure the tape is parallel to the floor. Enter this value in the “Bust Measurement” field.
3. Read Your Results: The calculator will instantly update, showing your estimated bra size, your band and cup sizes, a visual chart of your measurements, and a helpful sister size chart.
4. Use the Sister Size Chart: If your calculated size feels off, consult the sister size table. For example, if 34C feels too loose in the band, try a 32D. It has the same cup volume with a smaller band. Our bra size calculator makes this easy to see.

Key Factors That Affect Bra Fit

Beyond the measurements, several factors influence how a bra actually fits. A perfect result from a bra size calculator is a starting point, but you should also consider these:

• Band Snugness: The band should provide about 80% of the support. It should be snug and parallel to the floor. You should only be able to fit two fingers underneath it. If it rides up, it’s too loose.
• Cup Fit: Your breasts should be fully contained within the cups. There should be no “spillage” over the top (quad-boob) or gaps at the top of the cup. If the underwire sits on your breast tissue, you likely need a larger cup size.
• Gore Tacking: The center panel of the bra (the “gore”) should sit flat against your sternum without digging in. If it’s lifting away, the cups may be too small.
• Strap Tension: Straps are for stabilization, not for lifting. They should sit comfortably on your shoulders without digging in or slipping off. If they’re doing all the work, your band is likely too loose.
• Brand and Style Variation: Just like clothing, bra sizing is not standardized. A 34C in one brand might fit differently than in another. Similarly, a plunge bra will fit differently than a full-coverage bra. Always be prepared to try sister sizes.
• Breast Shape: Shape matters as much as size. Breasts can be shallow, projected, full on top, or full on bottom. Certain bra styles work better for specific shapes. For example, balconette bras are often great for shallower shapes.

Frequently Asked Questions (FAQ)

1. How often should I use a bra size calculator?
It’s a good idea to remeasure and use a bra size calculator every 6-12 months, or after any significant body changes like weight fluctuation, pregnancy, or starting a new fitness routine.

2. What if my measurements are between sizes?
This is very common. If your underbust is 31, the calculator will suggest a 32 band. However, depending on the brand’s stretchiness, you might try both a 30 and 32 band (using sister sizes like 30D and 32C).

3. Why do different bra size calculators give me different results?
Some calculators use different rounding methods or add inches to the underbust measurement (an older method). Our bra size calculator uses the modern, more accurate method of rounding to the nearest even number for the band and using the direct difference for the cup.

4. What is a “sister size”?
Sister sizes are alternative bra sizes with the same cup volume. To find a sister size, you go up one band size and down one cup size, or vice versa. For example, the sister sizes for a 34C are 32D and 36B. You can read more in our bra fitting guide.

5. Do I measure with or without a bra on?
For the most accurate result, measure while wearing a thin, non-padded, and non-compressive bra. This ensures your breasts are lifted to a natural position without adding extra volume.

6. My breasts are two different sizes. What should I do?
This is completely normal! Always fit the bra to your larger breast to avoid spillage and discomfort. You can use a small pad or “cookie” insert on the smaller side to even things out if you wish.

7. Can I use this bra size calculator for sports bras?
While this calculator gives a great starting point, sports bras often use S/M/L sizing and focus on compression. It’s best to consult the specific brand’s size chart, but knowing your true bra size will help you choose more accurately.

8. The calculator gave me a size I’ve never worn. Is it right?
It’s very possible! Since most people wear the wrong size, your calculated size might seem surprising (e.g., a smaller band and larger cup than you’re used to). We highly recommend trying on your calculated size and its sister sizes to see how they feel. This is a key step in using any bra size calculator effectively.