Yes you should take into account the height of the faucets. Normally a mirror would begin above them. (Think of what you want to reflect....lots of plumbing or the viewer?) You want to be low enough that a person who is 5' tall can easily see their entire face and chest. Typically that's going to be right above the faucet.

My powder room mirror is pushing the height limits at 45" above the floor. You don't want people to have to stand on their toes to see their face and chest. Mine is 4" above the faucet (so it's not crowded since mine opens). I'm sitting in a hotel right now and the mirror is right at faucet height (you don't see the faucet reflected in the mirror). I'd say it's about 38" off the floor. It's quite comfortable to use.

My higher mirror is a powder room mirror as well. I did a lot of research on the subject (suprising how much you can find on the internet) and the general concensus was that you should look to the short folks in society and cater to them for the bottom height, and the tall folks for the top height, so that someone 5' tall and someone else 6'4" will both feel comfortable in the room.

igloochic - Surprisingly, I hadn't considered the functionality of the mirror and its lower height! I was just worried about the space between the vanity top and bottom of mirror. With your ideas, I was able to validate with a 5'1" friend that she could still see in the mirror at the highest height. So thank you for bringing up those points.

In all your research did the recommend a distance between the vanity top/faucet top and bottom of mirror? If you miror did not open, would you have placed it lower?

Thanks