US Bra Size Calculator
Find your accurate bra size in minutes with our easy-to-use calculator and comprehensive fitting guide.
Measure snugly around your ribcage, just under your bust.
Measure loosely around the fullest part of your bust.
Your Estimated US Bra Size Is:
—
Enter your measurements to see results.
Understanding Your Bra Size
What is a US Bra Calculator?
A us bra calculator is a specialized tool designed to estimate your bra size based on two key body measurements: your underbust (band) and your bust. Finding the right bra size is crucial for comfort, support, and posture. While over 80% of women wear the wrong size, using a calculator is the first step toward finding a much better fit. This tool specifically uses standard US sizing conventions to determine your band number (e.g., 34, 36, 38) and cup letter (e.g., A, B, C, D).
This calculator is for anyone who is unsure of their current bra size, has experienced body changes, or feels their current bras are uncomfortable. It provides a reliable starting point for you to take to the lingerie store.
US Bra Calculator Formula and Explanation
The calculation for bra size is a two-step process. It's simple math, but the rules are very specific. The goal of this us bra calculator is to translate your body's dimensions into the standardized sizes used by manufacturers.
- Band Size Calculation: The band provides most of the bra's support. Your raw underbust measurement is 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 is still 32. If you measure 33 inches, you round up to 34.
- Cup Size Calculation: The cup size is determined by the difference between your bust measurement and your *calculated band size* (not your raw measurement). Each inch of difference corresponds to a cup letter.
Formula: Cup Difference = Bust Measurement - Calculated Band Size
Variables Table
| Variable | Meaning | Unit (auto-inferred) | Typical Range |
|---|---|---|---|
| Underbust Measurement | The measurement around your rib cage directly under your breasts. | Inches or cm | 26 – 50 in |
| Bust Measurement | The measurement around the fullest part of your breasts. | Inches or cm | 28 – 60 in |
| Cup Difference | The calculated difference that determines the cup letter. | Inches | 0 – 12 in |
Practical Examples
Example 1: Average Measurements
- Inputs:
- Underbust Measurement: 31.5 inches
- Bust Measurement: 37 inches
- Unit: Inches
- Calculation:
- Band Size: 31.5 rounds to 32.
- Cup Difference: 37 (Bust) – 32 (Band) = 5 inches.
- A 5-inch difference is a DD cup in US sizing.
- Result: 32DD
Example 2: Using Centimeters
- Inputs:
- Underbust Measurement: 85 cm
- Bust Measurement: 101 cm
- Unit: Centimeters
- Calculation:
- Underbust in inches: 85 cm / 2.54 = ~33.5 inches. Band size rounds to 34.
- Bust in inches: 101 cm / 2.54 = ~39.8 inches.
- Cup Difference: 39.8 (Bust) – 34 (Band) = ~5.8 inches.
- A 5.8-inch difference is close to a 6-inch difference, which is a DDD/F cup.
- Result: 34DDD (or 34F)
For more personalized advice, check out our bra fitting guide for tips on how different styles fit.
How to Use This US Bra Calculator
Using this calculator is simple and takes less than a minute once you have your measurements.
- Select Your Unit: Start by choosing whether you measured yourself in inches or centimeters from the dropdown menu.
- Enter Underbust Measurement: Type your snug ribcage measurement into the first field.
- Enter Bust Measurement: Type your loose bust measurement into the second field.
- Read the Results: The calculator will instantly update to show your estimated US bra size, your calculated band and cup, and the measurement difference.
- Interpret the Results: Use this size as your starting point. Remember to check our sister size charts if a bra is close but not perfect.
Understanding Sister Sizes
Sister sizes are a crucial concept in bra fitting. They are sizes that have the same cup volume but different band and cup letter combinations. Knowing your sister sizes can help you find a better fit if your calculated size isn't quite right. The rule is: if you go **up** one band size, you must go **down** one cup size to maintain the same cup volume.
Example: The sister sizes for a 34C are 32D (tighter band, larger cup letter) and 36B (looser band, smaller cup letter). They all hold roughly the same breast volume. Our guide on what are sister sizes explains this in more detail.
| Tighter Band | Your Size | Looser Band |
|---|---|---|
| 30C | 32B | 34A |
| 32D | 34C | 36B |
| 34DD | 36D | 38C |
| 36G | 38F(DDD) | 40E(DD) |
Key Factors That Affect Bra Fit
A calculator provides a great starting point, but several other factors influence the perfect fit.
- Brand and Style Variation: Just like clothing, bra sizing is not perfectly standardized. A 34C in one brand might fit differently than a 34C in another. Plunge, full-cup, and balconette styles also fit differently.
- Breast Shape: Your breast shape (e.g., round, slender, teardrop) affects how you fill out a cup. Some shapes work better with certain bra styles. Our guide for breast shapes can help.
- Band Tightness: The band should be snug and parallel to the floor. If it rides up your back, the band is too loose.
- Cup Spillage or Gaping: If your breasts spill out of the top or sides, the cup is too small. If there are gaps, the cup is too big or the wrong shape.
- Underwire Position: The underwire should sit flat against your rib cage and fully encase your breast tissue, not poke or sit on top of it.
- Hormonal Fluctuations and Weight Changes: Your body changes, and so does your bra size. It's wise to re-measure every 6-12 months.
Frequently Asked Questions (FAQ)
- 1. Is this us bra calculator accurate?
- It is highly accurate based on the standard measurement formula. However, it should be used as a starting point, as brand and style can affect the final fit.
- 2. What if my measurements are between sizes?
- If your band is between sizes, modern bras are stretchy, so it's often better to go with the smaller band for a snugger, more supportive fit. For cups, consider trying your calculated size and its sister sizes.
- 3. How do I know if my bra fits correctly?
- The band should be snug and level, the cups should fully contain your breast tissue without spillage or gaps, and the center panel (gore) should lie flat against your chest. The straps should not be doing all the lifting work.
- 4. Should I measure with or without a bra on?
- For best results, measure while wearing a non-padded, lightly-lined bra. If you don't have one, you can measure braless, but be careful to keep the tape level.
- 5. Why does my band ride up in the back?
- This is a classic sign that your band size is too big. The band is providing no support, forcing your straps to do all the work. Try a smaller band size (and likely a larger cup letter, your sister size).
- 6. What does it mean if the underwire pokes me?
- This usually means the cup size is too small, causing the wire to sit on breast tissue instead of your ribcage. It could also be the wrong style for your breast shape.
- 7. How often should I use a us bra calculator?
- You should remeasure yourself every 6 to 12 months, or after any significant weight changes, pregnancy, or starting a new hormonal medication.
- 8. Does cup size change with band size?
- Yes, absolutely. Cup volume is relative to band size. A 32D cup is much smaller than a 38D cup. This is why understanding sister sizing explained is so important.