After calculating the percentage for CAM charges for each tenant, how do I apply the CAM square footage to each Tenant's rentable space?

You take the total amount of the CAM charges for the entire shopping center/building and multiply it by the tenant's percentage. The amount you end up with is the amount that tenant pays for CAM.

joan38 agrees: I've always thought this was the correct way to calculate this but othes I know seems to do it different.

It's the basic way of doing it. But some people may use slightly different accounting methods. Or some tenants may have lease agreements that were negotiated a bit differently.