Thanks Druul!
For those wanting to calculate their own Bf value I have simplified the formula as much as possible and reduced it to using 3 base values.
Cp = the cup size of the individual expressed as 1 for A, 2 for B, 3 for C... fractions would work too, so a large C could be 3.75.
Ht = the height expressed as inches, sorry if you want it in metric cm just convert. 1 cm = 0.393701 in.
Fb = a calculated bra band factor which is the result of (18 - bra band in inches/2) so a Bd of 34 in. = (18-34/2) or a value of 1.
Now take those values and run them through this simplified equation:
{ [Cp + Fb - (3 - Cp) * (-50 * Fb) + 250 ] * Ht } / 100 * Bd + { Cp + [ Fb - (3 - Cp) ] } = BfBecause I have simplified the equation it does have to come with some limitations:
1) Accuracy starts to wane at band sizes above 44 or below 28, however most are within this range.
2) Accuracy starts to wane at cups above G cup, again most are within this range.
3) Totally irrational heights will yield irrational results so a 108" or 24" height will not mean anything.
4) Although it did not have any real significance, I have removed aspects of weight from the formula.
So any generic person you would normally meet could be used.
Think of this as a fancy ratio of bust to height to build when set against the average. Which is a value around 17 to 18.