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Being the curious types, we wanted to find out who invented the darned bra size measurement calculation that everyone dislikes so much!  Who thought up the idea to add 5″ to odd band measurements and 4″ to the even numbers?  Or, who even thought up measuring over the bust and subtracting the underbust?  Were they crazy?  Were they genius seamstresses?  Or, just math fantatics?  Well, the answer turned out to be anything but simple as there is not one person we can blame for the modern day bra size calculation!   What we did find out was just as interesting though….Read on.



S H Camp’s Advert in Feb 1933 Corset and Underwear Review

Back in the day when bras were in their infancy they were generally sold by the size of the person i.e. small, medium, large and relied on stretchable cups to accommodate sizes.  There is some debate over who actually invented the bra cup letter system that we use today – either William and Ida Rosenthal (founders of Maidenform), who apparently established the system in the 1920’s, or S H Camp & Co who first advertised the cup lettering system in Corset and Underwear Review in February 1933. In any case, this new bra measuring system correlated the ‘size and pendulousness’ of the breasts to letters, just four A, B, C and D. These letters weren’t linked to actual measurements though but the approximate degree of bust size. So if you had a small bust you’d choose an A and so on.

Warners Alphabet Bras 1940's

In 1937 Warners started using letters in their product descriptions

Maidenform Advert

This iconic Maidenform campaign ran for over 20 years!


Numbers for bra sizes were introduced some time after World War II. This number, however, did not refer to a band size or under bust measurement but to a full bust size which was used in conjunction with the cup designation i.e. if you measured 34 at the fullest part of your bust and felt that you had medium sized breasts you might be a 34B.


Sears Underwear Advert 1970's

Sears offering a ‘Custom Fit’ in the 1970’s!

In the 70’s there was a shift towards standardization. In 1975 the European Common Market put in place new regulations that changed the ‘number’ part of the bra size from a full bust measurement to a raw under bust measurement.  In the old system the number signified how large your breasts were so if you measured 34″ at full bust and had been buying a bra of that size your new ‘number’ might only be a 30″ since you were now measuring your rib cage, not the highest point of your breasts. This new system came with a lot of criticism!

It was from this change in the measuring method that the current way of calculating cup size seemed to emerge.   The new method focused on the difference between the raw under bust and the full bust measurements which were used to calculate your cup size.  Remember, previously the letter had merely referenced the approximate degree of bust size, now it had actual math behind it. The raw under bust measurement was subtracted from the full bust measurement and every inch difference between the two referenced a cup size i.e. 1″ difference = A cup, 2″ difference = B cup and so on.  Makes sense, right? This however opened up a whole new set of problems as, shock horror, not all women fit into the existing letter brackets. Some had less than an inch difference some had more than 6 inches!

NIPPLE BRA Advert 1970's

Strange that this ‘Nipple Bra’ didn’t take off!


What then seems to have happened, in the transition between the old and the new method, is two things.  First, manufacturers didn’t really change the range of sizes offered.  Secondly, because customers weren’t generally happy and possibly a little confused that they now had completely new bra sizes, manufacturers began telling women to add 4″ or 5″ to their raw under bust measurement, depending on whether it was odd or even. Doing this effectively allowed them to buy a bra with the same or similar ‘number’ to what they had always worn. Some people refer to this as ‘vanity sizing’.

40 years on we still use the add 4″ or 5″ calculation.  This system definitely creates unnecessary confusion for the customer when measuring (or being measured) and has caused some pretty strong feelings to be voiced with campaigns like War on Plus 4, started in 2012. War on Plus 4 basically pushes for all brands and fitters to use the raw under bust measurement as a starting point rather than adding on inches before a single bra has been tried on…now surely that’s just good sense!