Do colleges look at the weighted GPA and How do you calculate it?

It depends on the college. For example, Ohio State University does not take weighted grades into consideration. They go strictly by GPA, SAT, and here's the kicker--class ranking. OSU likes to accept only students in the top 25% of their class; so it is possible that a "better" student with a 3.3 in Honors/AP classes who ranks in, say, the 35th percentile, will be turned down in favor of the student with a 3.7 in basic coursework because he/she ranks in the upper 25% of the class.

My daughter graduated with a 3.7 (unweighted) GPA that included Honors classes. She did not get accepted to OSU's Columbus campus because her class rank was at around 30%. Even an OSU admissions rep admitted to my daughter's guidance counselor that they know their selection system is flawed because of this. But hey! OSU is big enough to do whatever it pleases.

It can be very confusing. I don't know what the steps are to adjust for weighted grades. It does seem unfair that some high schools weight grades while others do not and many colleges choose to ignore the distinction. The best thing to do is check with any colleges you're interested in to find out what their criteria are.

To respond to your addition:

Check with your school about rankings. By "ranking," I'm referring to the place your GPA holds in relation to the entire school. In other words, if there are 100 students in the junior class, and there are 36 students with a higher GPA than yours, your rank will be 37%. That's an oversimplification, but basically that's how it works.

Your high school may not place much emphasis on ranking, but I guarantee they will be able to provide that information to any college that asks for it.

you count +1 point into your gpa for any AP class you take. for example, lets say you take AP calculus and you passed it with an "A" then you get 5 point instead of 4.