Determining the swept area of braking surfaces

[Ghoste]

I know there are mathematical formulae for this and I can Google it as easily as ask here (unless someone knows what they are without looking it up) but for rotors, is it done based on the entire rotor surface or just the contact patch of the pads?  (for that matter, it should just be actual shoe width on drums as well no?)

[elacruze]

Only the surface area that makes contact with the pad is considered.

[Ghoste]

Okay thanks.  For some reason I was led to believe it was the entire machined surfaces of the drum and rotor.

[elacruze]

That could have been 'Marketing'. 

[Ghoste]

Possibly.   This question began started with a comment from a Chevy co-worker.