"Feet" is the plural form of "foot".
Student or Learner
What is the difference between "Foot" and "Feet"?
However, when giving someone's height, people will say six foot tall.
In the U.S. we would say "The guy is six feet tall" but "He's a six-foot-tall guy."
I'm not a teacher. I speak American English. I've tutored writing at the University of Southern Maine and have done a good deal of copy editing and writing, occasionally for publication.