How is Bra Size Calculator

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Reviewed by: David Chen, Lingerie Sizing Specialist

Ensuring comfort and accuracy through proven measurement methods.

Stop guessing your size! Use our professional Bra Size Calculator to accurately determine your band and cup size based on the two essential measurements. Simply enter your figures below and hit ‘Calculate’.

How Is Bra Size Calculated?

Your Estimated Bra Size:

Detailed Calculation:

    How Is Bra Size Calculated Formula

    Bra size is determined using two core measurements: the band size (calculated from the under-bust measurement) and the cup size (the difference between the over-bust and band measurements).

    BAND SIZE = Round(Under-Bust Measurement) + 4 (if even) or + 5 (if odd) (Simplified: Round up to nearest even number)
    CUP DIFFERENCE = Over-Bust Measurement – Band Size
    CUP SIZE = Letter corresponding to CUP DIFFERENCE (e.g., 1 inch = A, 2 inches = B)

    Formula Sources:

    Variables Explained

    The calculation requires two key inputs:

    • Under-Bust Measurement: The circumference measured tightly directly beneath the breast tissue. This is used to determine the Band Size (e.g., 34, 36).
    • Over-Bust Measurement: The circumference measured loosely around the fullest part of the bust (typically across the nipples). This measurement is used to determine the Cup Size.

    What is Correct Bra Sizing?

    Correct bra sizing is crucial for health and comfort. A well-fitting bra provides the necessary support to prevent back, neck, and shoulder pain, and helps maintain breast shape. Studies show that over 80% of women wear the wrong size, often leading to discomfort or poor posture.

    The “Band Size” should be firm and level, bearing 80% of the support. The “Cup Size” should fully encapsulate the breast tissue without spillage or gaping. Our calculator provides a starting point, but fit can vary between brands.

    How to Calculate Bra Size (Example)

    Follow these steps using hypothetical measurements:

    1. Initial Measurements: Under-Bust = 30.7 inches; Over-Bust = 35.5 inches.
    2. Calculate Band Size: Round the Under-Bust (30.7) up to the nearest even number. 30.7 rounds up to 32 inches. This is the band size.
    3. Calculate Cup Difference: Subtract the Band Size from the Over-Bust Measurement: 35.5 in – 32 in = 3.5 inches.
    4. Determine Cup Letter: A difference of 3 inches is a ‘C’ cup, and 4 inches is a ‘D’ cup. A 3.5-inch difference suggests a ‘C/D’ or ‘D’ depending on the brand. Our calculator uses a standard chart: 3 inches = C, 4 inches = D.
    5. Final Result: The resulting size is approximately 32D.

    Frequently Asked Questions (FAQ)

    Here are common questions about bra sizing:

    • Why do I need to measure both my under-bust and over-bust?
      The under-bust determines the band size, which provides the majority of the support. The difference between the over-bust and the band measurement determines the cup size, which dictates volume.
    • What is the +4/+5 method, and is it accurate?
      The traditional +4/+5 method is an older sizing technique that adds inches to the under-bust. Many modern fitters prefer a more direct, tighter measurement method (rounding to the nearest even number) for a firmer, more supportive fit.
    • Why do my bra sizes vary between brands?
      Sizing consistency, often called ‘vanity sizing’ or ‘manufacturer variance,’ means that the exact fit of a 34C can differ slightly across different lingerie brands, styles, and countries (US, UK, EU).
    • Should I measure myself while wearing a bra?
      No. To get the most accurate measurements, you should measure yourself while wearing only a thin, unpadded, non-compressing bra, or completely nude.

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