Comp City, Second Edition by Max Rubin, pg 21.
Based on the assumptions of 60 hands per hour, 2% house advantage and 40% of estimated loss paid in comps, the result is 48% of average bet per hour. The example shows how a $100 average bet yields $48 in comps.
Also, if you follow Mr. Cant's advice and do a google.com search, you will most likely find many websites providing the same information. I did so, but I leave it up to you to find out for yourself. Search for "casino comp calculation".
This is an unpaid, unshilled, endorsement of Comp City. It is an indispensable reference for anyone interested in playing for comps.