Bra Size Calculator
An estimated 80% of women wear the wrong bra size. Find your accurate size in two simple steps for better comfort, support, and confidence.
Calculate Your Size
Your Estimated Bra Size
Calculated Band Size
—
Calculated Cup Size
—
Bust – Band Difference
—
Formula: Cup Size is determined by subtracting the Band Size from the Bust Measurement. Each inch of difference corresponds to a cup letter.
Visualizing Your Measurements
Understanding Sister Sizes
If a bra in your calculated size doesn’t feel right, you might have better luck with a “sister size.” These are alternate sizes where the cup volume is the same. The rule is: if you go up one band size, go down one cup size, and vice versa. Our bra size calculator helps you find a starting point, but sister sizes give you more options.
| Go Down a Band Size (Tighter Band, Larger Cup) |
Your Size | Go Up a Band Size (Looser Band, Smaller Cup) |
|---|---|---|
| 32D | 34C | 36B |
| 34D | 36C | 38B |
| 36D | 38C | 40B |
What is a Bra Size Calculator?
A bra size calculator is a digital tool designed to help you determine your most accurate bra size based on specific body measurements. By inputting your band (underbust) and bust (fullest part) measurements, the calculator processes these numbers to provide a recommended band number and cup letter. An accurate bra size calculator is the first step in solving common fit issues like gaping cups, slipping straps, and tight bands.
This tool is for anyone who wears a bra and feels they might not have the correct fit. It’s especially useful if you’ve recently experienced bodily changes due to weight fluctuation, pregnancy, or hormonal shifts. A common misconception is that bra sizes are static, but they can change multiple times throughout your life. Regularly using a bra size calculator ensures you always have the best support.
Bra Size Calculator Formula and Mathematical Explanation
The mathematics behind a bra size calculator are straightforward and involve two key steps: determining the band size and then the cup size.
- Band Size Calculation: This measurement is taken snugly around the ribcage, right under the bust. A common traditional method (which this calculator uses) is to take the measurement in inches, round it to the nearest whole number, and then if the number is even, add 4 inches, and if it’s odd, add 5 inches. This result is your band size (e.g., 34, 36, 38).
- Cup Size Calculation: This is found by subtracting your calculated band size from your bust measurement (taken at the fullest point). The resulting difference in inches determines your cup letter.
For example: If your bust measurement is 37 inches and your calculated band size is 34, the difference is 3 inches. A 3-inch difference typically corresponds to a ‘C’ cup. Therefore, the bra size is 34C.
Variables Table
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Underbust Measurement | The measurement around the ribcage directly under the breasts. | Inches | 26 – 45 |
| Bust Measurement | The measurement around the fullest part of the bust. | Inches | 30 – 55 |
| Band Size | The numbered part of the bra size, representing the frame size. | Inches (Even Numbers) | 30 – 50 |
| Cup Size Difference | Bust Measurement – Band Size. This determines the cup letter. | Inches | 0 – 12+ |
Practical Examples (Real-World Use Cases)
Example 1: Average Measurements
- Inputs:
- Underbust Measurement: 31 inches
- Bust Measurement: 37 inches
- Calculation:
- Band Size: 31 (odd) + 5 = 36
- Cup Difference: 37 (bust) – 36 (band) = 1 inch
- Result: 36A
- Interpretation: This person should start by trying a 36A bra. If the band feels too loose, they could try a sister size down: 34B. A good bra fitting guide can provide more tips.
Example 2: Fuller Bust Measurements
- Inputs:
- Underbust Measurement: 34 inches
- Bust Measurement: 41 inches
- Calculation:
- Band Size: 34 (even) + 4 = 38
- Cup Difference: 41 (bust) – 38 (band) = 3 inches
- Result: 38C
- Interpretation: The recommended starting size is 38C. It’s important to ensure the gore (the center part of the bra) sits flat against the sternum. Understanding the sister size chart is also key here; a 36D or 40B might offer a better fit depending on body shape. This is where a bra size calculator proves invaluable.
How to Use This Bra Size Calculator
- Gather Your Tool: You’ll need a soft, flexible measuring tape.
- Measure Your Band: While wearing a non-padded bra (or no bra), measure around your ribcage directly under your bust. The tape should be snug and level. Enter this number into the “Band Measurement” field of the bra size calculator.
- Measure Your Bust: Measure around the fullest part of your bust. The tape should be loose enough that it doesn’t compress your breast tissue. Enter this into the “Bust Measurement” field.
- Read Your Results: The bra size calculator will instantly display your estimated bra size, including your calculated band and cup size.
- Make a Decision: Use this calculated size as your starting point when shopping. Remember to also consider the sister sizes shown in the table for more flexibility. Our how to measure bra size guide has more details.
Key Factors That Affect Bra Size Results
Your bra size isn’t just about two numbers. Several factors can influence the fit and what size you should ultimately choose. A good bra size calculator gives you a baseline, but consider these points:
- Breast Shape: Breasts come in many shapes (e.g., round, east-west, slender, bell-shaped). Some bra styles (like a plunge or balconette) work better for certain shapes.
- Brand and Style Variation: Just like with clothing, bra sizing can vary significantly between brands. You might be a 34C in one brand and a 34D in another.
- Time of the Month: Hormonal fluctuations during your menstrual cycle can cause breasts to swell, potentially changing your cup size temporarily.
- Age of Your Bra: Bras stretch out over time. An old, stretched-out bra will not fit the same as a new one, even if they are labeled as the same size. The band provides most of the support, and once its elasticity is gone, the fit is compromised.
- Weight Changes: Gaining or losing even a small amount of weight can affect both your band and cup size. It’s wise to remeasure yourself or use a bra size calculator after any significant body changes.
- Pregnancy and Postpartum: Pregnancy and breastfeeding cause major changes in breast size and sensitivity, often requiring a move to different sizes and bra types (like nursing bras). Getting a professional fitting or using a reliable bra size calculator during this time is essential.
Frequently Asked Questions (FAQ)
- 1. How often should I use a bra size calculator?
- It’s recommended to measure yourself and use a bra size calculator every 6-12 months, or after any significant life event like pregnancy or weight change.
- 2. What if my measurements are between numbers?
- Always round to the nearest whole number. If you’re consistently between sizes, understanding your sister size chart is the best way to find a comfortable fit.
- 3. The calculator gave me a size I’ve never worn before. Is it right?
- It’s very likely. Since most women wear the wrong size, a correct measurement can often seem surprising. Trust the bra size calculator as a new starting point and be open to trying on the recommended size.
- 4. Does cup size stay the same across band sizes?
- No. Cup volume is relative to the band size. A 32D cup is smaller in volume than a 36D cup. This is why sister sizing is so important. A 32D has the same cup volume as a 34C and a 36B.
- 5. Can I use this bra size calculator for sports bras?
- While it provides a good starting point for your overall size, sports bras often use S/M/L sizing and are categorized by impact level. Check the brand’s specific size chart after getting your base measurement from a bra size calculator.
- 6. What are the signs of a poor-fitting bra?
- Common signs include straps digging in or slipping off, the band riding up your back, cups gaping or overflowing, and the underwire poking or sitting on your breast tissue instead of your ribcage.
- 7. What does the number and letter in a bra size mean?
- The number (e.g., 36) is the band size, which is the measurement of your torso. The letter (e.g., C) is the cup size, which represents the volume of your breasts relative to your band size. Our bra cup size calculator section explains this in more detail.
- 8. Why does the band feel tight even if the measurement is right?
- It could be that your cup size is too small. If your breasts aren’t fully in the cups, they can steal space from the band, making it feel tighter. Try going up a cup size before you change the band. A proper fit is key, so using a bra size calculator is a great first step.