FL?
I agree with DFC , you take off pressure above 1013(QNH/SAS) thats the golden rule. so assuming 3000ft 1015 , wind off 2 millibars 2940ft therefore round up and you get FL30.
As DFC says it doesnt mean you a sep from other traffic just a means to fly, dont get me going on ATC sep! I try to do it daily!
NM