Thirdlove Bra Size Calculator

Discover your perfect fit with the official ThirdLove bra size calculator. An accurate bra size is the first step to comfort and support. Follow the steps below to find your size.

Your Recommended Bra Size

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Calculated Band Size: —

Bust-Band Difference: —

Your sister sizes are — and —.

Visual representation of your measurements.

What is a ThirdLove Bra Size Calculator?

A ThirdLove bra size calculator is a specialized tool designed to help you determine your most accurate bra size based on your unique body measurements. Unlike generic calculators, this tool uses a method closer to how professional fitters work, focusing on the two key measurements that define bra fit: your band size (the number, like 34) and your cup size (the letter, like C). Finding the right size is crucial for comfort, support, and health, and this calculator is the first step in ending the search for a bra that actually fits. It serves as an excellent starting point before exploring tools like our Fit Finder® Quiz for more nuanced recommendations.

This calculator is for anyone who has struggled with common bra fit issues like gaping cups, slipping straps, or a digging band. By providing a precise, data-driven starting point, the ThirdLove bra size calculator empowers you to shop with confidence.

ThirdLove Bra Size Calculator Formula and Explanation

Our calculator simplifies the complex process of bra fitting into two steps. The calculation method is designed for modern bras, which have more stretch than vintage ones, so we don’t add extra inches to the band measurement.

1. Band Size Calculation: Your band size is determined by your underbust measurement. We take your snug underbust measurement and round it to the nearest whole number. If that number is odd, we add one to get to the next even number. If it’s already even, that is your band size. This ensures the band is snug enough to provide 80% of the bra’s support.
2. Cup Size Calculation: Your cup size is found by subtracting your final band size from your fullest bust measurement. The resulting difference in inches corresponds to a cup letter.

Bra Size Calculation Variables

Variable	Meaning	Unit	Typical Range
Underbust Measurement	The circumference of your ribcage directly beneath your bust.	Inches or cm	26 – 48 in (66 – 122 cm)
Fullest Bust Measurement	The circumference of your chest at the fullest point of your bust.	Inches or cm	28 – 56 in (71 – 142 cm)
Bust-Band Difference	Fullest Bust – Band Size. This difference determines the cup volume.	Inches	0 – 9 inches

Cup Size Chart (based on difference)

Difference (inches)	Cup Size
<1″	AA
1″	A
2″	B
3″	C
4″	D
5″	DD (E)
6″	DDD (F)
7″	G
8″	H
9″	I

Practical Examples

Let’s walk through two common scenarios to see how the ThirdLove bra size calculator works.

Example 1:

• Inputs:
  • Underbust Measurement: 31.5 inches
  • Fullest Bust Measurement: 37 inches
• Calculation:
  1. Band Size: 31.5 inches is rounded to 32. Since 32 is an even number, the band size is 32.
  2. Cup Size: 37 inches (fullest bust) – 32 (band size) = 5 inches.
• Result: A 5-inch difference corresponds to a DD cup. The final recommended size is 32DD.

Example 2:

• Inputs:
  • Underbust Measurement: 89 cm
  • Fullest Bust Measurement: 104 cm
• Calculation (after conversion to inches):
  1. 89 cm is approx. 35 inches. 104 cm is approx. 41 inches.
  2. Band Size: 35 inches is rounded to 35. Since 35 is an odd number, we add 1, making the band size 36.
  3. Cup Size: 41 inches (fullest bust) – 36 (band size) = 5 inches.
• Result: A 5-inch difference corresponds to a DD cup. The final recommended size is 36DD. To better understand how different styles fit, check our guide to different bra styles.

How to Use This ThirdLove Bra Size Calculator

1. Select Your Unit: Start by choosing whether you’ll be entering your measurements in inches or centimeters.
2. Measure Your Underbust: Wrap a soft measuring tape snugly around your ribcage, right under where your bra band sits. Make sure the tape is level all the way around and exhale to get the smallest measurement. Enter this number into the “Underbust Measurement” field.
3. Measure Your Fullest Bust: Now, wrap the tape around the fullest part of your bust (usually at the nipple level). The tape should be loose enough that it doesn’t compress your breast tissue. Enter this number into the “Fullest Bust Measurement” field.
4. View Your Results: The calculator will instantly display your recommended band size, cup size, and final bra size. It will also show you your “sister sizes,” which are alternative sizes that may also fit you well. Knowing about sister sizing can give you more options when shopping.

Key Factors That Affect Bra Fit

Your calculator size is a great starting point, but several other factors can influence your perfect fit. The ThirdLove bra size calculator gets you close, but always check these details when trying on a new bra.

• Band Fit: The band should be snug and level. You should only be able to fit two fingers underneath it. If it rides up, it’s too loose.
• Cup Fit: Your breasts should fill the cups completely with no spilling over the top or sides (too small) and no gaping or empty space (too big).
• Strap Fit: Straps should sit comfortably on your shoulders without slipping off or digging in. They provide only 20% of the support; the rest comes from the band.
• Gore (Center Panel) Fit: The center panel of the bra between the cups should lie flat against your sternum without gaping or digging.
• Breast Shape: Shape matters as much as size. Breasts can be round, teardrop, asymmetrical, etc. Some bra styles, like our Classic T-Shirt Bra vs. a Plunge Bra, work better for specific shapes.
• Changes Over Time: Body weight fluctuations, hormonal changes, and age can all affect your bra size. It’s a good idea to re-measure every 6-12 months.

Frequently Asked Questions (FAQ)

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

We recommend measuring yourself every 6 to 12 months, or after any significant life changes such as weight loss/gain, pregnancy, or starting a new fitness routine. Your body changes, and your bra size can too!

2. Is this bra size calculator accurate?

Yes, this ThirdLove bra size calculator provides a highly accurate starting point based on standard measurement guidelines. However, it’s a starting point. Your perfect fit can also depend on breast shape and the style of the bra.

3. What if my measurements are between sizes?

This is very common! Our calculator rounds to determine your band size. Your best bet is to try your calculated size and its sister sizes. For example, if you measure as a 34C, also try a 32D (smaller band, larger cup) and a 36B (larger band, smaller cup).

4. Why doesn’t this calculator add 4 inches to my band?

The “add 4 inches” method is an outdated technique from a time when bras didn’t have elastic materials. Modern bras are designed to stretch, so adding extra inches results in a band that is too loose and unsupportive.

5. What is a sister size?

Sister sizes are groups of bra sizes with the same cup volume. For example, a 34C, 32D, and 36B are sister sizes. If a bra feels too tight in the band, you can go up a band size and down a cup size (e.g., from 34C to 36B). Learn more in our Guide to Sister Sizing.

6. My calculator result is different from what I currently wear. Why?

Studies show over 80% of women wear the wrong bra size. Your current bra might be the wrong size, even if you’re used to it. We recommend trusting the measurement and trying on your recommended size from the ThirdLove bra size calculator.

7. Does cup size change with the band size?

Yes, cup sizes are not static. A ‘C’ cup on a 32 band is smaller in volume than a ‘C’ cup on a 36 band. This is why sister sizing works.

8. How do I know if my bra fits correctly?

Check for the five key signs of a perfect fit: a snug band, cups that don’t gape or overflow, a flat center gore, comfortable straps, and a smooth silhouette under clothing. Our Perfect Fit Guide has more details.