The goal post must be a minimum of 20 feet above the crossbar and the crossbar is 10 feet above the ground, so that would make the top of the goal post a minimum of 30 feet above
http://wiki.answers.com/Q/What_is_the_height_of_go...

1. Mark two PVC pipes and cut them into two pieces: one 4foot piece and one 6foot piece. Mark and cut two more pieces, creating one 2foot piece and one 8foot piece. 2. Secure
http://www.ehow.com/how_5631985_buildfootballgoa...

NFL & NCAA goal posts are 10 feet high & 18 feet, 6 inches
http://www.chacha.com/question/whatistheheight...

There is only a minimum on the length of the uprights. It is 20 feet above the crossbar. They uprights can into infinity, but 20 feet is the minimum.
http://answers.yahoo.com/question/index?qid=200809...
