Quantifying A Bra’s Effect on Bust Girth



A quick fit of a range of cup sizes in any bra style soon proves the urban myth of a change in cup size changing bust girth by one inch wrong.


After years of struggling with the dynamic nature of bust girth in evening wear design I set out on a quest to discover…

  1. Where the myth of bust girth increasing by one inch with cup size originated from.
  2. Why inaccurate bra size prediction methods continued to be used.
  3. Why there appeared to be discrepancies between global bra sizing methodologies.
  4. Why a change in overbreast did not correlate to a change in bust girth.
  5. How cup size could be incorporated in garments.

My first two years of research were spent reverse engineering product lines looking for the common ground on which to base a new bra size prediction method.  Two anomalies inhibited my research; discrepancies in global sizing parameters, and the correlation between breast mound growth and bust girth.  Upon closer examination I came to understand that conversion error and grade variations were causing numerical global differences.  Once these discrepancies were accounted for, an underlying global sizing systems became clear and the hemispherical breast model presented itself.  This was my first major breakthrough and the foundational common ground for bra sizing that I had been looking for.  

The second breakthrough in my research came with an understanding that the development of the bra had created two sub-categories of garments; encapsulated and non-encapsulated.  As I came to understand that vintage bras were made from non-encapsulated garment patterns concerned with visual cup size while modern bras are made from encapsulated garment patterns concerned with actual cup size the synergy between two opposing sizing systems became clearer.  As much as this understanding was a breakthrough however, it was also a trap that relentlessly pulled me into another three years of research.

The diagram to the right illustrates the relevance of my research.  The illustrations depict cup sizes “A to E” manipulated to create the same bust girth.  The overbreast measurements of the cups  vary according to standard measurements but the volume of the different cups is manipulated such that the bust girth measurement remains static throughout the manipulations.  The bust and underbust girth of these five different cup sizes are all the same so the VISUAL cup size will also be the same.  The overbreast measurement, however, clearly indicates that there are five different cup sizes.

The bust and underbust girth of these five different cup sizes are all the same so the VISUAL cup size will also be the same.  The overbreast measurement, however, clearly indicates that there are five different cup sizes.  Due to the malleability of breast volume and the dynamic nature of apex spread, the bust girth associated with breast mounds is also dynamic.

Non-encapsulated garments are constructed for a static bust girth but encapsulated garments change the bust girth.  For example, a manufacturer will associate a certain bust girth with garment size such as 95cm for a size 10 garment because bust girth is static.  This is not the  case with encapsulated garments such as bras.  A 36C bra my create a bust girth of 95cm in one bra style and a bust girth of 90cm in another.


Defining the relationship between the static non-encapsulated garment bust girth and the dynamic encapsulated garment bust girth is complicated but possible.


Understanding the difference between visual and actual cup size is the first step in understanding the relationship between breast, bra and garment.  The next crucial step is understanding how the manipulation of a 3D breast relates to a 2D pattern.  The theory behind that reflects six years of research soon to be released in my book “Breast, Bra, Garment: The Mathematical Models Behind Sizing and Fit.”  

The book explains …

  1. The hemispheric breast model.
  2. How to predict cup shape for desired volume manipulation.
  3. How to analyze a 3D volume to predict the 2D pattern outcomes.
  4. The intricate interplay between bra cup shaping, containment diameter and apex spread that contribute to bust girth.
  5. How breast mound volume manipulation will affect bust girth and consequently garment fit.

 The webpage Bra and Garment Synergy discusses the topic of bra and garment synergy further.


Contact me to discuss integrating these methodologies into your CAD platforms or to be put on the first to notify list when this book becomes available.


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