Mowing height is one of the simplest things you can change to improve a lawn, and it costs nothing. Grass cut too short has shallow roots, dries out fast and lets weeds move in. Grass left a little taller shades the soil, stays greener in heat and chokes out weeds. This mowing height calculator gives you the best height for your grass type, and tells you how tall the grass can get before it needs cutting.
How to use the mowing height calculator
- Choose your grass type. If you are unsure, check the type of grass in our growing zone finder or ask a local garden center.
- Pick your conditions. In hot, dry weather or in shade, raise the mower half an inch above the normal height.
- Read the result. It shows the recommended height, the height at which to mow and the most you should cut off at once.
The math behind it
Mow when height = target height × 1.5
Most you remove = one third of the grass height
Worked example: Kentucky bluegrass
The calculator picks 3 in as the middle of the 2.5 to 3.5 in range. The grass should be mowed when it reaches 4.5 in, which removes 1.5 in, exactly one third of the blade.
Worked example: Bermudagrass in summer heat
The normal range is 1 to 2 in, so the target is 1.5 in. In hot, dry conditions the range moves up half an inch to 1.5 to 2.5 in, for a target of 2 in and a mowing trigger of 3 in.
The one-third rule
Never remove more than about one third of the grass blade in a single mowing. Cutting more than that stresses the plant, because the leaves feed the roots. If the lawn has grown too tall, raise the mower and bring it down gradually over a couple of mowings instead of scalping it at once.
Typical heights by grass
- Kentucky bluegrass: 2.5 to 3.5 in.
- Tall fescue: 3 to 4 in.
- Fine fescue: 2.5 to 3.5 in.
- Perennial ryegrass: 2 to 3 in.
- Bermudagrass and zoysiagrass: 1 to 2 in.
- St. Augustinegrass: 2.5 to 4 in.
- Centipedegrass: 1.5 to 2 in.
- Buffalograss: 2 to 3 in.
These are typical extension ranges. Varieties differ, and some modern dwarf varieties tolerate shorter cutting.
Mowing tips that help
- Keep the blade sharp. A dull blade tears the grass and leaves brown tips.
- Leave the clippings. Short clippings break down quickly and return nutrients, which cuts the fertilizer you need. See our fall lawn fertilizer calculator.
- Mow dry grass when you can, for a cleaner cut.
- Change the pattern each time to avoid ruts and a lean in the grass.
- Raise the height before a heat wave or drought, and mow a little lower in the cool part of the season.
Frequently asked questions
What is the best height to mow a lawn?
For most cool-season lawns, about 3 inches. Warm-season lawns such as Bermudagrass and zoysia are kept shorter, around 1 to 2 inches.
How often should I mow?
Whenever the grass reaches about one and a half times your target height. In fast spring growth that may be every few days, and in summer heat or drought it may be every week or two.
Does cutting grass short make it grow slower?
No. Short grass has less leaf to feed its roots, so it is weaker. Taller grass grows deeper roots and handles drought better.
What if I missed a mowing and the grass is too tall?
Raise the mower and cut off no more than a third. Wait a few days, lower the blade a notch and mow again until you reach your target height.