What Does The Letter And Number Mean In Bra Size

Complete Explanation

A bra size is typically expressed as a number followed by a letter, such as 34C or 38B. The number represents the band size, which is the circumference of the torso measured just below the bust, usually in inches. The letter represents the cup size, which indicates the difference between the full bust measurement and the band measurement. Each inch of difference corresponds to one cup size increment: for example, a 1-inch difference is an A cup, 2 inches is B, 3 inches is C, and so on. However, cup volume is not absolute; it scales with band size, so a 34C holds a smaller volume than a 36C.

• Band Size (Number):
  Measured around the ribcage directly under the bust. In US/UK sizing, it is the measurement in inches (e.g., 32, 34, 36). If the measurement is an odd number, fitters often round up to the next even number. The band provides most of the bra’s support.
• Cup Size (Letter):
  Calculated by subtracting the band measurement from the bust measurement. The resulting difference determines the letter: less than 1 inch = AA, 1 inch = A, 2 inches = B, 3 inches = C, 4 inches = D, 5 inches = DD/E, 6 inches = DDD/F, etc. Many sizing systems extend beyond D cup, but notations vary between countries.
• Sister Sizing:
  Bra sizes are not fixed; a 34C and a 36B have the same cup volume but different band lengths. This relationship, known as sister sizing, allows for alternative fits when a bra band feels too tight or too loose.
• Measurement Method:
  Standard practice involves taking two measurements: a snug underbust (for band) and a loose overbust at the fullest part of the chest. Professional fitters also consider breast shape and brand variations.

History / Background

The concept of bra sizing emerged in the early 20th century. Before the 1930s, bras were sold by bust circumference only, with little differentiation for cup volume. In 1935, Warner’s introduced the first cup-size system with four categories: A, B, C, and D, based on the difference between bust and underbust measurements. This innovation allowed for more individualized fit. Over subsequent decades, additional cup sizes were added (DD, DDD, etc.) to accommodate a wider range of body types. The modern standard, using a number for band and a letter for cup, became widespread after World War II. Different regions developed their own conventions: for example, many European countries use centimeter-based band measurements, and cup progressions (A, B, C, …) may differ in increments (e.g., 2 cm rather than 1 inch).

Importance and Impact

Standardized bra sizing has had a significant impact on the lingerie industry and consumer comfort. It provides a common language for manufacturers, retailers, and customers, enabling mass production of bras that fit a spectrum of body shapes. The system helps reduce guesswork when shopping, though fit variability remains high due to differences in brand scaling, fabric stretch, and breast shape. Research indicates that a large percentage of women wear incorrectly sized bras, often because they are unaware of how the number-letter combination translates to actual fit. The sizing system also influences related products like sports bras, swimwear, and shapewear.

Why It Matters

Understanding bra size notation helps individuals make informed purchasing decisions, leading to better comfort, support, and health. An ill-fitting bra can cause shoulder pain, back strain, skin irritation, and breast tissue damage. Knowing how to measure accurately and interpret the number-letter code empowers consumers to find bras that provide adequate support—especially important for larger busts where proper fit affects posture and mobility. Additionally, awareness of sister sizing can save time when a preferred band size is unavailable.

Common Misconceptions