how to monitor the RAM of any Windows Server in % not MB form with SCOM

hello,

We have some  Windows Server where RAM on these servers are allocated with Dynamically Start-up so that it auto growth the RAM size according to requirement dynamically. I wants to how to monitor these Servers RAM  such a way that when RAM usage more then 50% threshold crossed it  will throw alerts.But where I know currently Monitoring of Memory Utilization with SCOM on Available Mega Bytes of Memory works on  free MB not % Basics.

Thanks 
Richa KM