You can order Cisco 5500 Series Controllers with support for 12, 25, 50, 100, 250 or 500 APs as the controller's base capacity. You can add additional AP capacity through capacity adder licenses available at 25,
50, 100 and 250 AP capacities. You can add the capacity adder licenses to any base license in any combination to arrive at the maximum capacity of 500 APs.
Reference: http://www.cisco.com/c/en/us/support/docs/wireless/5500-series-wireless-controllers/112926-5508-wlc-license.html