Converting Total Available Memory Value to Percentage

Long time reader, first time poster!!

We are trying to edit our "Total Available Memory (MB)" component in "Windows Server 2003-2012 Services and Counters" template to convert the value from MB to a percentage value.

Now, I was thinking it would have to be a long statement, but, here is what I generally think would need to happen:

Memory Value in MBminusTotal Memory in MBdivided by 100

Is this even possible? I would prefer to base my critical/warning values off of a percentage in the template. I hope I was clear in my question.

I'm open to suggestions as well. Any help is good help!

Thanks Community!