It actually varies among manufacturers (often by a lot) but a 32x11.50R15 is generally around 31.5 x 11.0
A quick and easy way to compare tire sizes is go to Tirerack.com and look at tires. They list sizes as spec'd by the manufacturers, not from some calculator. Example: http://www.tirerack.com/tires/Spec.j...irePageLocQty=
And if you are shopping online and their system won't take the 32x11.50 measurement, go elsewhere. Who knows what you will get. With a real tire retailer will be able to find the actual sizes of the tires you are looking at and not have to "convert" to something else.