Fescue mowing height
The general rule of thumb for determining what the grass height should be on your lawn for a cool-season grass generally is between 3 inches to 4 inches. Only remove about the top 1/3 of the grass blade at one time.
A mowing height between 3 - 3 1/2 inches is best for most of the season, except during summer stresses when the lawn mowing height should be raised to mow at 3 1/2 - 4 inches.
Raising the mowing height provides more insulation from summer heat and reduces water loss from your soil.