📏 Accurate Bra Size Calculator (International)

🎯 What is the Bra Size Calculator?

The **Bra Size Calculator** is a precision tool that translates two fundamental body measurements—**Underbust** and **Overbust**—into accurate bra sizes across various international standards, including US, UK, EU, and French sizing. The purpose is to address the common issue of ill-fitting bras by providing a scientifically derived starting size.

💡 Why You Need This Tool and Its Purpose

Over 80% of individuals wear the wrong size bra, leading to discomfort, poor posture, and compromised garment lifespan. This calculator serves two main purposes:

1. **Accuracy:** It removes guesswork by implementing proven sizing algorithms (such as the +4 method and sister sizing principles).
2. **Global Shopping:** It simplifies purchasing from international brands or stores by instantly converting your primary size (e.g., UK) into the required system (e.g., EU).
3. **Self-Assessment:** Helps users monitor changes in their body size over time, ensuring they purchase the correct size every time they shop.

⚙️ How This Calculator Works: Band and Cup Calculation

Bra size is a composite measure, consisting of a **Band Number** and a **Cup Letter**.

1. Calculating the Band Size:

The band size is determined by the underbust measurement.

• **UK/US (The +4 Method):** If the underbust measurement in inches is an even number, add 4 inches. If it's an odd number, add 5 inches. *Example: 30" underbust becomes a 34 band.* This ensures a snug, supportive fit.
• **EU/Continental:** This system uses the underbust measurement rounded to the nearest multiple of 5 centimeters. *Example: 73 cm underbust becomes a 75 band.*

2. Calculating the Cup Size:

The cup size is determined by the **difference** between the **Overbust** (fullest part of the bust) and the **Band Size**. $$ \text{Cup Difference} = \text{Overbust Measurement} - \text{Band Measurement} $$ In the US/UK system, every 1-inch (2.54 cm) difference corresponds to one cup size.

2.1. Understanding Cup Progression (AA, A, B...):

The cup letter indicates the volume difference relative to the band size. The progression is typically:

• **AA:** Less than 1 inch (or less than 2.5 cm) difference. Indicates a very small difference between the underbust and overbust measurement.
• **A:** 1 inch (2.54 cm) difference.
• **B:** 2 inch (5.08 cm) difference.
• **C:** 3 inch (7.62 cm) difference.
• **D:** 4 inch (10.16 cm) difference.
• **DD / E:** 5 inch (12.7 cm) difference.

3. International Conversion Summary:

The calculator uses precise formulas to map the calculated US/UK size to other systems: