You know, it really depends on the place. Some places will _screw_ you because of % and in some places it will be a great help.
Having said that you can't convert a GPA from your year's averages. You must convert EACH course mark into a GPA. Usually, the conversion goes like this:
90% or over: A+ , 4.3 (if the place uses 4.3 scale, otherwise 4)
85-89%: A, 4
80-84: A-, 3.7
77-79: B+, 3.3
73-76: B, 3
70-72: B-, 2.7
67-69: C+, 2.3
63-66: C, 2
60-62: C-, 1.7
50-59: D, 1
0-49: F, 0
This is in general. Not every school will do it in exactly this way but this is a rough outline.