There are different levels of wai, based on how much one lowers the head. This depends on who we're greeting. The more respect we have for the person or the more senior the person is, the more we bend the head.
These are general guidelines on how much we should bend the head while greeting. They form the three basic wais that Thais have used until today:
1. Don't bend the head at all. Just put your hands together in front of your chest by putting your left palm flat against your right palm. We make this gesture when someone who's junior or younger wai us.
2. Follow the process in 1 and bend your head down until the tip of your nose touch the tips of your index fingers. We do this to elders or more senior people.
3. Follow the process in 1 and bend your head down until the tips of your thumbs touch the area between your eyebrows. When greeting monks, women do this gesture after lowering the body by bending the knees while men lower the upper body and wai.