Bra Size Calculator

Professional Tools for Informed Decisions

An accurate, easy-to-use tool to find your perfect bra size.

Results Analysis & Visualization

Your Sister Size Chart

Go Down a Band Size (Tighter Band, Larger Cup)	Your Calculated Size	Go Up a Band Size (Looser Band, Smaller Cup)
—	—	—

Sister sizes have the same cup volume. If your band feels too tight or loose, a sister size may provide a better fit.

What is a Bra Size Calculator?

A Bra Size Calculator is a tool designed to estimate a person’s bra size based on two primary measurements: the underbust and the bust. Finding the correct bra size is crucial for comfort, support, and overall health, yet many individuals wear the wrong size. This calculator uses a standard formula to convert your body measurements into a suggested band and cup size, providing a reliable starting point for finding the perfect fit.

This tool is for anyone who wears a bra and wants to ensure they are choosing the right size. It’s especially useful if you’ve experienced changes in body weight, after pregnancy, or if you simply feel your current bras are uncomfortable. Common misunderstandings often relate to how band and cup sizes work together, which is where a bra size calculator and the concept of sister sizing become invaluable.

The Bra Size Formula and Explanation

Bra sizing is based on two components: the band size and the cup size. The formula is straightforward:

1. Band Size: This is determined by your underbust measurement. The raw measurement is typically rounded to the nearest even number to get the band size (e.g., 31 inches becomes a 32 band).
2. Cup Size: This is calculated by finding the difference between your bust and underbust measurements. Each inch of difference corresponds to a letter in the cup alphabet.

The core formula is: Cup Size = Bust Measurement – Underbust Measurement.

Formula Variables

Variable	Meaning	Unit (Auto-Inferred)	Typical Range
Underbust	The measurement around the ribcage just beneath the breasts.	Inches / Centimeters	26 – 48 in (66 – 122 cm)
Bust	The measurement around the fullest part of the breasts.	Inches / Centimeters	28 – 55 in (71 – 140 cm)
Difference	Bust minus Underbust. Determines the cup letter.	Inches / Centimeters	1 – 10 in (2.5 – 25 cm)

Practical Examples

Example 1: Average Measurements

• Inputs: Underbust = 31 inches, Bust = 36 inches
• Units: Inches
• Calculation:
  • Band size is determined from the 31″ underbust, which rounds to 32. (Some systems add inches, but modern methods often use the rounded underbust).
  • The difference for the cup is 36″ (Bust) – 32″ (Calculated Band) = 4 inches.
• Result: A 4-inch difference corresponds to a ‘D’ cup. The final size is 32D.

Example 2: Using Centimeters

• Inputs: Underbust = 85 cm, Bust = 102 cm
• Units: Centimeters
• Calculation:
  • First, convert to inches: 85 cm ≈ 33.5 in; 102 cm ≈ 40.2 in.
  • The underbust of 33.5″ rounds up to a band size of 34.
  • The difference for the cup is 40.2″ (Bust) – 34″ (Band) ≈ 6.2 inches.
• Result: A 6-inch difference corresponds to an ‘F’ cup (US sizing). The final size is 34F. Our Bra Size Calculator handles these conversions for you.

How to Use This Bra Size Calculator

1. Select Your Units: Start by choosing either ‘Inches (in)’ or ‘Centimeters (cm)’ from the dropdown menu. The calculator will automatically adjust.
2. Enter Underbust Measurement: Using a soft measuring tape, measure around your ribcage right below your bust line. The tape should be snug but not tight. Enter this number in the “Underbust Measurement” field.
3. Enter Bust Measurement: Measure around the fullest part of your bust. Ensure the tape is level across your back and not too tight. Enter this value into the “Bust Measurement” field.
4. View Your Results: The calculator will instantly display your calculated bra size, including the band and cup. It will also show intermediate values and a chart visualizing your proportions.
5. Check Sister Sizes: The table below the main result shows your sister sizes. These are alternative sizes that have the same cup volume and might offer a better fit if the band of your calculated size feels off.

Key Factors That Affect Bra Fit

A Bra Size Calculator provides an excellent starting point, but several other factors influence the final fit:

• Brand and Style Variation: Sizing is not perfectly standardized across brands. A 34C in one brand might fit differently than in another. Styles like plunges, full-cups, and balconettes also fit differently.
• Breast Shape: Shape (e.g., round, teardrop, wide-set) is as important as size. Some bra styles are better suited for certain shapes.
• Band Snugness: The band should provide about 80% of the support. It should be snug and parallel to the floor. If it rides up, it’s too loose.
• Cup Fit: There should be no gapping at the top of the cup or spillage at the sides or top. The underwire should sit flat against your sternum.
• Strap Adjustment: Straps should be adjusted to be comfortable without digging into your shoulders. They only provide about 20% of the support.
• Material and Age of Bra: Bras stretch over time. A new bra should fit snugly on the loosest hook, allowing you to tighten it as it ages. Materials also affect stretch and support.

Frequently Asked Questions (FAQ)

1. What are sister sizes?

Sister sizes are related bra sizes with the same cup volume. If you go down a band size, you go up a cup size to maintain the volume (e.g., 34C has the same cup volume as 32D). This is useful if your calculated size’s band is too loose or tight.

2. How often should I measure myself?

It’s a good idea to remeasure your bra size every 6-12 months, or after any significant life event like weight change, pregnancy, or starting a new fitness regimen.

3. The calculator gave me a size I’ve never worn. Is it right?

It’s very common! Many people are surprised by their calculated size because they’ve been wearing ill-fitting bras for years. Trust the measurements as a new starting point and try on bras in and around your calculated size and its sister sizes.

4. Does this calculator work for all countries (US, UK, EU)?

This calculator primarily uses the US/UK sizing system where each inch of difference is one cup size. European (EU) sizing can be different. Always check a brand’s specific size conversion chart if you are buying from an international brand.

5. Why is the band size so important?

The band provides the vast majority of the support. An incorrect band size is the most common reason for a poor-fitting bra. If the band is too loose, all the strain falls on the shoulder straps, leading to discomfort.

6. Can I measure myself while wearing a bra?

For the most accurate results, you should measure yourself while wearing a non-padded, non-minimizer bra, or no bra at all. This ensures the measurements reflect your natural shape.

7. What if I’m between two sizes?

If you’re between sizes, consider your breast shape and the style of the bra. Trying a sister size is often the best solution. For example, if a 34C cup fits well but the band is too loose, try its sister size down: 32D.

8. How is breast volume calculated?

While this calculator determines size by measurements, true breast volume is a complex medical calculation involving methods like the Archimedes principle (water displacement) or 3D imaging. Bra cup sizes are a simplified, commercial proxy for volume.

Related Tools and Internal Resources

Understanding your body is key to wellness. Explore these other calculators to get a more complete picture of your health and fitness metrics.

• BMI Calculator – Check if your weight is in a healthy range for your height.
• Body Fat Calculator – Estimate your body fat percentage, a key indicator of fitness.
• Pregnancy Due Date Calculator – An essential tool for expecting mothers.
• Calorie Calculator – Determine your daily calorie needs for weight maintenance, loss, or gain.
• Ideal Weight Calculator – Find your healthy weight range based on different formulas.
• Bra Size Conversion Chart – Convert your size between US, UK, EU, and other international sizing systems.