Tires: Tire Markings, tire markings, tire rack

Question
What do the numbers mean on a tire that says 30x9.50 R15.  Is it comparable to a P275/75 R15?  
Thanks.

Answer
Gene,

I was hoping that Tire Rack had a short article on the subject - but they don't.

A 30X9.50R15LT is 30" in diameter, 9 1/2" wide, and fits on a 15" rim, and is a "Light Truck" tire.

The conversion to P metric tires doesn't quite work, but it is sort of equivalent to P255/75R15 - a non-existent size.