When it comes to mowing your lawn, the 1/3 rule is key. As the name suggests, this method means you only ever remove one-third of the grass blade’s height when you’re mowing. Rossi says the 1/3 rule allows most people to mow “about 25% to 35% less frequently.” Below, we explain how the 1/3 rule works and why it’s worth trying. To do that and still follow the 1/3 rule, they will need to cut the lawn when it reaches 3 inches.