What size of air compressor do I need?

by Jerry
(Hazleton , PA)

I have a air grinder that operates at 90 psi. What size of air compressor do I need to run it for a while?

I have alot of different air tools and even though I only use one at a time my air compressor will always run low on air in about 2 - 3 minutes. How big of an air compressor do I need to keep the tool going for at least one hour?