Bra Size Measurements Calculator

The first step to comfort and support is finding your correct size. Use our tool to calculate your bra size based on your unique measurements.

Your Measurements Visualized

A visual comparison of your underbust and bust measurements. This chart updates in real-time.

How to Use This Bra Size Measurements Calculator

Finding your bra size is a simple process with our calculator. Follow these steps for an accurate result:

1. Select Your Units: Choose between inches or centimeters from the dropdown menu. The calculator will automatically convert as needed.
2. Enter Underbust Measurement: Measure around your ribcage, just beneath your breasts. The tape should be snug and parallel to the floor. Enter this number into the “Underbust Measurement” field.
3. Enter Bust Measurement: Measure around the fullest part of your chest, typically across the nipples. Ensure the tape isn’t too tight. Enter this value into the “Bust Measurement” field.
4. View Your Results: The calculator instantly displays your calculated bra size, including your band size and cup letter, as you type.
5. Interpret the Chart: The bar chart provides a visual representation of your measurements, helping you see the difference that determines your cup size.

What is a Bra Size Measurements Calculator?

A bra size measurements calculator is a tool designed to translate your body measurements into a standard bra size. Since statistics show that a high percentage of women wear the wrong bra size, using a calculator is an essential first step toward finding a comfortable and supportive fit. This is especially crucial for online shopping, where you can’t try items on. The calculator uses two key inputs: the underbust (band) measurement and the bust measurement, to determine your band and cup size. Understanding these two components is the key to decoding bra sizes.

Bra Size Formula and Explanation

Bra sizing can seem confusing, but it’s based on two simple calculations. Our bra size measurements calculator uses a common method to determine your size.

1. Band Size Calculation: The band is the numerical part of your bra size (e.g., 34 in 34C). It’s derived from your underbust measurement. A widely used method involves adding 4 or 5 inches to your raw underbust measurement to get the final band size.
   • If your underbust measurement (in inches) is an even number, add 4 inches.
   • If your underbust measurement is an odd number, add 5 inches.

   Formula: Calculated Band Size = Round(Underbust Measurement) + (4 or 5)

2. Cup Size Calculation: The cup is the letter part of your size (e.g., C in 34C). It represents the volume of your breasts relative to your band size. It’s found by subtracting the final calculated band size from your bust measurement.
   
   Formula: Cup Difference = Bust Measurement – Calculated Band Size

The resulting difference in inches corresponds to a letter. For example, a 1-inch difference is an ‘A’ cup, a 2-inch difference is a ‘B’ cup, and so on.

Formula Variables

Variable	Meaning	Unit	Typical Range
Underbust Measurement	The circumference of the ribcage directly under the breasts.	Inches or cm	26 – 48 in (66 – 122 cm)
Bust Measurement	The circumference over the fullest part of the bust.	Inches or cm	30 – 55 in (76 – 140 cm)
Calculated Band Size	The final band number, adjusted from the underbust measurement.	Inches (Size)	30 – 52
Cup Difference	The difference between the bust and the calculated band size.	Inches	0 – 12 in

Practical Examples

Let’s see how the bra size measurements calculator works with some real-world numbers.

Example 1: Using Inches

• Inputs:
  • Underbust Measurement: 31 inches
  • Bust Measurement: 37 inches
  • Unit: Inches
• Calculation:
  1. Band Size: The underbust is 31 (an odd number), so we add 5. 31 + 5 = 36. The band size is 36.
  2. Cup Size: Subtract the new band size from the bust measurement. 37 – 36 = 1 inch difference.
• Result: A 1-inch difference corresponds to an ‘A’ cup. The final bra size is 36A.

Example 2: Using Centimeters

• Inputs:
  • Underbust Measurement: 80 cm
  • Bust Measurement: 99 cm
  • Unit: Centimeters
• Calculation:
  1. Convert to Inches: First, convert measurements to inches (1 inch = 2.54 cm).
     • Underbust: 80 cm / 2.54 = 31.5 inches
     • Bust: 99 cm / 2.54 = 38.98 inches
  2. Band Size: Round the underbust to 32 (an even number), then add 4. 32 + 4 = 36. The band size is 36.
  3. Cup Size: Subtract the new band size from the bust measurement. 38.98 – 36 = 2.98 inches difference (which rounds to 3 inches).
• Result: A 3-inch difference corresponds to a ‘C’ cup. The final bra size is 36C.

Understanding Sister Sizes

A “sister size” is a bra size that has the same cup volume as your true size, but with a different band size. This is a crucial concept for finding a better fit when your usual 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, and vice versa.

For example, if a 36C feels too loose in the band, you could try its sister size down: 34D. The 34D will have a tighter band but the same cup volume as the 36C.

Sister Size Chart Example for 36C

Go Down in Band (Tighter)	Your Size	Go Up in Band (Looser)
34D	36C	38B
32DD	34D	36C

Sister sizes allow you to find an equivalent cup volume on a different band size.

Key Factors That Affect Bra Size

Your calculated bra size is a starting point. Several factors can influence how a bra actually fits:

• Brand and Style: Sizing is not perfectly standardized across brands. A 34C in one brand might fit differently than in another. Similarly, a plunge bra fits differently than a full-coverage bra.
• Measurement Accuracy: Measuring yourself correctly is critical. A tape that is too tight or too loose can skew your results. Always measure while standing straight and breathing normally.
• Time of the Month: Hormonal fluctuations can cause breasts to swell, temporarily changing your size.
• Weight Changes: Gaining or losing even a small amount of weight can affect both your band and cup size.
• Age of Your Bra: Over time, a bra’s elastic band stretches out. A bra that once fit perfectly on the loosest hook may become too loose even on the tightest hook.
• Breast Shape: Shape (e.g., round, slender, teardrop) can affect how you fill out a cup, even if your volume matches the size. Some bra styles are better suited for specific shapes.

Frequently Asked Questions (FAQ)

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

It’s a good idea to measure yourself every 6 to 12 months, or whenever you experience significant life changes like weight loss/gain, pregnancy, or starting a new exercise regimen.

2. What if my calculator result seems wrong?

The calculator provides a starting point based on a popular formula. If the size feels off, trust your body. Use the concept of sister sizes to adjust. If the band is too tight but the cups fit, go up a band size and down a cup size (e.g., from 34C to 36B).

3. Why do I need to add 4 or 5 inches to my underbust measurement?

This traditional method, known as the “+4 method,” was created to align with older sizing standards. While some modern brands use the raw underbust measurement as the band size, the +4 method is still widely used and provides a good baseline for many popular brands.

4. My breasts are different sizes. Which one should I measure?

This is very common. Always fit your bra to the larger breast to avoid spilling out of the cup. You can then use a small insert or “cookie” in the cup of the smaller breast to create a symmetrical look.

5. What do DD and DDD mean?

After D, cup sizing can vary. In the US, the next sizes are typically DD (equivalent to E in the UK) and DDD (equivalent to F in the UK). Our calculator uses the common US convention where 1″=A, 2″=B, 3″=C, 4″=D, 5″=DD, 6″=DDD/F.

6. Does the calculator work for all countries?

This calculator primarily uses the US/UK sizing system based on inches. While it converts cm to inches for the calculation, the final size (e.g., 34C) is standard in the US and UK. European sizes are different (e.g., 75C).

7. How do I fix straps that dig in or slip off?

Digging straps often mean your band is too loose and not providing enough support, forcing the straps to do all the work. Try a smaller sister size (e.g., 34D instead of 36C). Slipping straps can mean the band is too tight, or you may need a style with more centered straps, like a racerback.

8. What are the signs of a poor-fitting bra?

Common signs include the band riding up your back (band too loose), spillage over the top or sides of the cups (cups too small), gaping in the cups (cups too large), or the underwire digging into your skin.