You will be surprised how well it covers. You don't want a whole lot because it will work in reverse and not do its job. You can Google application of thermo compound and see what I mean!
EDIT: Read this.
http://www.arcticsilver.com/pdf/appinstruct/as5/ins_as5_intel_dual_wcap.pdf
I also use coffee filters to clean the cpu and heatsink because it is lint free.