The answer to this question depends on a number of factors, including the type of grass, the time of year, and the desired length of the grass. In general, it is best to wait until the grass is about six inches tall before cutting it. This will give the roots time to establish themselves and create a dense network of blades. If the grass is cut too short, it will be more susceptible to damage from foot traffic and pests. However, if the grass is allowed to grow too long, it can become difficult to mow and may develop brown patches. As a result, it is important to find a balance that works for your particular lawn. With a little trial and error, you will be able to find the perfect height for your grass.