Bra Size Calculator

Finding a comfortable, supportive bra is essential for daily posture, shoulder relief, and clothing comfort. However, because manufacturer scales and regional sizes vary, finding the correct fit can be challenging. Many people find themselves wearing uncomfortable sizes simply due to outdated measuring rules.

Our free online Bra Size Calculator calculates your ideal size based on two quick measurements, supporting sizing systems for the United States/Canada, the United Kingdom, continental Europe, France/Belgium/Spain, and Australia/New Zealand:

• Standard Bra Size Calculator: Input your bust and band measurements to find your estimated size in your chosen regional system.
• Bra Size Converter: Instantly convert a known size (e.g., a US 34D) into its equivalent size across other global systems.

To ensure accuracy, measure using a soft tape to the nearest 1/4 inch or 1/2 centimeter.

Signs of an Incorrect Bra Fit

Surveys indicate that between 70% and 85% of women wear incorrectly fitted bras. The lack of global standardization means sizes can vary between brands, making a single measurement more of a starting point than a final answer.

The most common fitting error is choosing a back band that is too large combined with a cup size that is too small. If you experience any of the following symptoms, your bra may not be fitting correctly:

• The back band digs into your ribs, leaves red marks, or slides up your shoulder blades.
• The shoulder straps dig in, causing neck, shoulder, or back pain (meaning the straps are carrying the weight instead of the band).
• Your breasts overflow around the top or sides of the cups.
• The center panel (the gore) does not lie flat against your breastbone.
• The underwires pinch or dig into the sides of your breast tissue.

How to Measure Band and Bust Sizes

To find your correct size, take two measurements while standing straight with your arms relaxed at your sides, preferably wearing a thin, unpadded underwire bra:

1. Band Size (Frame Size): Wrap the measuring tape firmly (but not tightly) around your ribcage directly underneath your breasts.
2. Bust Size: Wrap the tape loosely around the fullest part of your chest, ensuring the tape remains level across your back.

International Band Size Conversion Table

Band sizes are labeled differently around the world. The table below outlines standard band size conversions across regional systems:

Calculating Cup Sizes by Bust-Band Difference

Cup size is determined by the difference between your bust and band measurements. The table below matches these differences to US, UK, and European cup sizes:

To check other lifestyle indicators, visit our BMI Calculator. To compute base caloric metrics, use the BMR Calculator, or track pregnancy cycles with our Pregnancy Calculator.

Frequently Asked Questions (FAQ)

What is “sister sizing” in bras?

Sister sizing refers to group sizes that share the same cup volume even though their band and cup letters differ. If you go down one band size (e.g., 36 to 34), you must go up one cup size (e.g., C to D) to maintain the same cup volume. Thus, a 36C and a 34D are sister sizes.

How often should I measure my bra size?

Lingerie fitters recommend measuring your size at least once a year, or whenever you experience significant weight fluctuations, pregnancy, or changes in your exercise routine, as small changes in body composition alter your support needs.

Why does my bra band keep sliding up my back?

If your bra band slides up your back, the band is too large. The band should fit snugly and level around your ribcage, parallel to the floor, as it provides 80% of the bra’s support. Try going down one band size and up one cup size to maintain support.

Are sports bra sizes different from regular bras?

High-impact encapsulation sports bras use standard band and cup sizes to provide structured support. Compression-style sports bras typically use general S, M, L sizing formats, which are less precise and rely on general torso measurements.