ThirdLove Bra Calculator
Find your perfect bra size with our easy-to-use calculator. Get an accurate fit recommendation in seconds.
Measure snugly around your ribcage, just under your bust. The tape should be level.
Measure around the fullest part of your bust. Don’t pull the tape too tight.
Your Recommended Bra Size
Calculated Band Size: —
Bust-Band Difference: — inches
Calculated Cup Size: —
Your Measurement Profile
Find Your Sister Sizes
| Band Down / Cup Up | Your Size | Band Up / Cup Down |
|---|---|---|
| — | — | — |
What is a ThirdLove Bra Calculator?
A thirdlove bra calculator is a specialized tool designed to help you find your most accurate bra size based on two key measurements: your underbust and overbust. Unlike generic calculators, the thirdlove bra calculator methodology accounts for unique body shapes and the brand’s signature half-cup sizes, aiming for a superior fit. This tool is for anyone who has struggled with uncomfortable bras, inconsistent sizing between brands, or is unsure how to measure themselves correctly. A common misconception is that bra size is static, but in reality, it can change multiple times throughout your life due to hormonal shifts, weight changes, and age. Regularly using a thirdlove bra calculator can ensure you’re always wearing the best size for your body right now.
ThirdLove Bra Calculator Formula and Mathematical Explanation
The calculation behind the thirdlove bra calculator is a two-step process that determines your band and cup size. The logic is straightforward but precise, especially with the inclusion of half-cup sizing.
Step 1: Determine Your Band Size
Your band size is derived from your underbust measurement. You measure around your ribcage, and that number is rounded to the nearest whole number. Then, a value is added to determine the band. ThirdLove’s method simplifies this by directly correlating the rounded underbust to a band size. For example, an underbust measurement of 30.5 to 31.5 inches typically corresponds to a 34 band size.
Step 2: Determine Your Cup Size
Your cup size is found by subtracting your final band size from your bust measurement. Each inch of difference corresponds to a cup letter. The key innovation in the thirdlove bra calculator is acknowledging the half-inch. A 2.5-inch difference, for example, results in a B½ cup, providing a more nuanced fit than traditional sizing.
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Underbust | The measurement around the ribcage directly under the breasts. | Inches | 28 – 45 |
| Overbust | The measurement around the fullest part of the bust. | Inches | 30 – 55 |
| Difference | Overbust minus Band Size. This determines the cup letter. | Inches | 0 – 9 |
Practical Examples (Real-World Use Cases)
Example 1: Finding a Standard Size
Someone measures their underbust at 31 inches and their overbust at 36 inches. Using the thirdlove bra calculator, the 31-inch underbust rounds to a 34 band. The difference between the overbust (36″) and the new band size (34″) is 2 inches. This 2-inch difference corresponds to a B cup. Their recommended size is 34B.
Example 2: Finding a Half-Cup Size
Another person has an underbust of 29.5 inches and an overbust of 35.5 inches. The thirdlove bra calculator logic would place their band size at 32. The difference between the overbust (35.5″) and the band (32″) is 3.5 inches. This lands them perfectly in a C½ cup, a size they might not find with other brands. Their final size would be 32C½.
How to Use This ThirdLove Bra Calculator
- Measure Your Underbust: Using a soft measuring tape, measure around your ribcage, directly under your bust. The tape should be snug but not tight. Enter this value into the “Underbust Measurement” field.
- Measure Your Bust: Measure around the fullest part of your bust. The tape should be level and not too tight. Enter this number into the “Bust Measurement” field.
- Read Your Results: The calculator will instantly display your recommended bra size, including band and cup. It will also show key intermediate values like the bust-band difference.
- Check Your Sister Sizes: The table below the main result shows your sister sizes. If your calculated band feels a bit off but the cup volume is right, a sister size calculator can provide a great alternative fit.
Key Factors That Affect ThirdLove Bra Calculator Results
- Posture During Measurement: Slouching can alter your measurements. Stand up straight with your shoulders back for the most accurate numbers.
- Time of the Month: Hormonal fluctuations, especially during a menstrual cycle, can cause breasts to swell. For consistency, it’s best to measure when your breasts are in their “normal” state.
- Type of Measuring Tape: Always use a soft, flexible measuring tape (like one for sewing). A rigid metal tape measure will not provide accurate results.
- Measurement Tightness: The underbust measurement should be snug, while the overbust measurement should be looser, just skimming the body. Pulling too tight on either can skew your results. For more tips, see our full bra fitting guide.
- Breast Shape: Your breast shape (e.g., athletic, relaxed, side set) can affect how a bra fits, even in the correct size. Our Breast Shape Dictionary can help you find styles tailored to your shape.
- Age and Life Changes: Pregnancy, breastfeeding, weight gain or loss, and menopause all have a significant impact on breast size and tissue. It’s wise to re-measure with a thirdlove bra calculator every 6-12 months.
Frequently Asked Questions (FAQ)
It is highly accurate, especially when you provide precise measurements. It’s designed to mirror an expert fitting by using a proven formula, including ThirdLove’s signature half-cup sizes for a better fit.
This is where half-cup sizes and sister sizes are invaluable. If your measurement difference is on a half-inch, our calculator will suggest a half-cup. If the band is the issue, check the sister size chart for an alternative.
We recommend re-calculating your size every 6-12 months or after any significant body changes (like pregnancy or weight fluctuation) to ensure you maintain a perfect fit.
The “+4 method” is an outdated technique from when bras were made with less elastic material. Modern bras don’t require it, and adding inches often leads to a band that is too loose and unsupportive. Our thirdlove bra calculator uses a modern, more accurate method.
While this calculator gives you a very reliable starting point for any brand, it is optimized for ThirdLove’s specific sizing, including half-cups. Sizing can vary slightly, so you may need to adjust. A great tool for comparison is a universal bra size chart.
Sister sizes are bra sizes that have the same cup volume. For example, a 34C has the same cup volume as a 32D and a 36B. Knowing your sister size is useful if a store doesn’t have your exact size or if you need a different band fit.
Slipping straps are often a sign that your band is too loose. A properly fitted band should provide 80% of the support. If the band rides up your back, it’s too big, causing the straps to fall. Try a smaller sister size (down in band, up in cup).
Both are equally important for a perfect fit. The thirdlove bra calculator gives you the correct size, but understanding your breast shape helps you choose the right style (e.g., plunge vs. full coverage) for your unique body. Explore our best fitting bras for different shapes.
Related Tools and Internal Resources
- Fit Finder® Quiz: For an even more personalized recommendation, this quiz analyzes your current fit issues and breast shape.
- Wireless Bras Collection: Explore our comfortable and supportive wireless options once you know your size.
- Breast Shape Dictionary: Learn about different breast shapes and which bra styles are most flattering for each.
- Common Bra Fit Issues and How to Solve Them: A guide to troubleshooting problems like gaping cups or digging bands.
- Easy Returns & Exchanges: Our policy ensures you can find the perfect fit without stress.
- Bra Size Conversion Charts: Compare your size across different international sizing systems.