Bicycle Brake Pads

I was wondering how thick pads of disc brakes on my bike have been when they were brand new. The brakes are on my bike brakes are Avid BB5 mechanical. I wonder what the total thickness of the material and the brake backing plate is?

I would like to order a set of brake pads on the line for a good price if you have them when you need it. Think of it as a spare tube, you have when you need it. I have spare chains, brake pads, master links, and cables just in case I need it. I buy them when they are on sale and several at once.