This calculator uses the latest community-verified “A Bra That Fits” (ABTF) measuring standards for optimal accuracy.
Welcome to the definitive **A Bra That Fits Calculator**. By utilizing six key measurements, this tool provides a highly accurate starting size based on the popular ABTF methodology, moving beyond traditional two-measurement systems.
A Bra That Fits Calculator
Detailed Calculation Steps
Enter your measurements and click ‘Calculate’ to see the detailed breakdown.
A Bra That Fits Calculator Formula
The ABTF method derives the band and cup size through averaging multiple bust measurements to account for breast shape and projection. This provides a more consistent result than single-measurement methods.
1. Average Bust (AvgB) = (Standing Bust + Leaning Bust + Lying Bust) / 3
2. Band Size (BND) = Snug Underbust rounded to the nearest even number (UK/US sizing)
3. Cup Differential (Diff) = AvgB - BND
4. Cup Size = Diff (in inches) mapped to UK Cup Progression (1=A, 2=B, 4=D, 5=DD, etc.)
Formula Sources: A Bra That Fits Community (UK) | Reddit r/ABraThatFits Wiki
Variables Used in the Calculator
- Loose Underbust: Measured loosely while breathing normally. Used as a reference for comfort.
- Snug Underbust: Measured firmly but not tight while breathing out normally. This measurement dictates the final band size.
- Tight Underbust: Measured as tightly as possible on a full exhale. Used to check for minimum band stability.
- Standing Bust: Measured while standing upright at the fullest point of the bust.
- Leaning Bust: Measured while leaning over 90 degrees. Captures the fullest projection without gravity interference.
- Lying Bust: Measured while lying flat on your back. Accounts for tissue migration.
Related Calculators
Explore other tools to perfect your fit and size conversions:
- US to UK Bra Size Converter
- Sister Size Calculator
- Underwire Width Calculator
- Bust-to-Waist Ratio Calculator
What is A Bra That Fits Calculator?
The “A Bra That Fits Calculator” is an advanced online tool designed to provide a highly accurate starting bra size recommendation. It originated from the r/ABraThatFits community and solves the common problem of ill-fitting bras resulting from outdated two-measurement systems (band and bust only).
Unlike traditional methods, the ABTF calculator uses six measurements to accurately gauge the average bust volume across different positions (standing, leaning, and lying). This sophisticated approach accounts for breast projection, density, and shape, leading to a much better starting point for finding a comfortable and supportive bra.
How to Calculate a Bra Size (Example)
Follow these steps using hypothetical measurements:
- Collect Measurements: Assume Snug Underbust (SUB) = 33.5 in, Standing Bust (SB) = 40 in, Leaning Bust (LB) = 41 in, Lying Bust (LyB) = 39 in.
- Determine Band Size: The SUB of 33.5 is rounded to the nearest even number, which is 34. Band Size = 34.
- Calculate Average Bust: $(40 + 41 + 39) / 3 = 120 / 3 = 40$ inches. Average Bust = 40 in.
- Calculate Cup Differential: Average Bust minus Band Size: $40 – 34 = 6$ inches. Differential = 6 in.
- Determine Cup Size: A 6-inch difference corresponds to a UK size E (or DD/F depending on specific system). In the standard ABTF progression, it’s 6 inches = E.
- Final Recommended Size: 34E (UK).
Frequently Asked Questions (FAQ)
Is the ABTF calculator always 100% accurate?
No calculator is 100% accurate due to individual variations in breast tissue density and shape. The ABTF result is a strong starting point. It may require slight size adjustments (e.g., a sister size) based on how a specific bra style fits you.
Why do I need six measurements instead of two?
The six-measurement system is crucial because it accounts for projection. Measuring the bust in different positions (standing, leaning, lying) helps determine the true volume, leading to a more accurate cup volume recommendation than traditional methods.
What is ‘sister sizing’?
Sister sizes have the same cup volume but a different band size. For example, a 34C is the sister size of a 32D and a 36B. It’s often used if the calculated size has a perfect cup but an uncomfortable band.
Should I use my tight or snug measurement for the band?
The Snug Underbust is generally used as the basis for the Band Size. The Tight Underbust is a check to ensure the chosen band size is supportive enough and doesn’t sit too high, but the snug measurement is the primary driver.