When cutting your grass it is always best to leave your grass at the highest possible setting which could be anywhere from 3 inches to 3 1/4 inches in height. When leaving the grass longer this creates more shade on the lawn, which will allow the lawn to retain more water and help prevent weeds from spreading. It is very important to remember the 1/3 rule that applies to grass as well as plants you should never cut more than one-third of the blade of grass. In wet weather when the grass grows faster this is when you need to be careful about not cutting too short some people who cut back more than one third or go below 2 1/2 inches are destined to burn and damage the lawn