A couple of days ago I ran into a tweet with a reference to A Sophisticated pair's bra calculator, and good comments along with it.
I am a strong believer that bra calculators are a flawed concept, but they are better than nothing when properly executed, it is just hard to run into one that doesn't try to do anything clever turning them into terrible advice.
So I took a look at their calculator to see how they do it, here's the math:
Here be Math
They take a couple measurements, band and bust measurement, both in inches.
For the ribcage they go straight to business, if your measurement is an even number, then that is your band size. Right on!
If your back measurement is an odd number, you can choose between a snug or loose band fit, then it will add or subtract one to get an even number, and suggest that as a band.
|Snug fit||Looser fit|
|Even number||Measurement is your band size|
|Odd number||+1 to get your band size||-1 to get your band size|
For the cups, they round your bust measurement (0.5 and up goes to the next round number up) and then do a simple difference between bust and band. AA being for equal measurements and up to LL cup for 18" difference using UK's cup sizing.
Any numbers outside of that range will show the error "Error! Please re-enter your measurements.".
This calculator has some pretty simple math, and it seems to be yielding good results without doing anything strange.
The downside, is that they don't do any band verification, so you will get suggestions for bands 18, 4, 10 if you enter that number, or mistakenly enter centimeters data.