Yeah, it's not really a fair comparison.
To calculate your unweighted GPA on a 4.0 scale, use the following system:
4 = A, 3 = B, 2 = C, 1 = D, F = 0 (and I highly doubt that you have any of the last three)
So add those up for each semester of each class you've had and then divide by the total number of classes. If you've gotten A's in every single class, then it's a 4.0. If you've gotten mostly A's and a few B's, it should be really close to 4.0.