How to measure the slope of your yard
Mark off 10 feet along the hill, measure how far the ground drops over that run, and divide the drop by 10 feet. Multiply by 100 and you have your percent.
What you need
A tape measure, a yardstick or any straight stick you can stand upright, and a level (a phone level app will do). A helper makes it faster, but a stake in the ground works as the second person.
Steps
- Pick the steepest stretch. Not the average. Walk the yard and find the spot that feels worst under your feet.
- Anchor the tape at the top. Have your helper hold the end of the tape on the ground at the top of that stretch, or weigh it down with a stake or a shoe.
- Walk 10 feet downhill in the direction the ground falls, pulling the tape out as you go.
- Stand the yardstick up at the bottom. Hold the tape against it and raise or lower your hand until the tape is level. Check with the level.
- Read the drop. It is the height on the yardstick where the level tape touches. A drop of 3 feet over 10 feet of run is a 30% slope. This is the method the University of Georgia describes.
- Do it in three places along the steepest stretch and use the biggest number.
Skip the arithmetic
Enter a drop to see your slope.
Percent versus degrees
Mower makers mostly rate slopes in percent, sometimes with degrees beside it. Phone level apps often read degrees. They are not the same scale: 100% is only 45 degrees, because percent is rise over run and a 45-degree hill rises exactly as far as it runs. The chart below converts the common ones.
| Percent | Degrees | Drop over 10 feet |
|---|---|---|
| 5% | 2.9° | 0.5 ft |
| 10% | 5.7° | 1.0 ft |
| 15% | 8.5° | 1.5 ft |
| 20% | 11.3° | 2.0 ft |
| 27% | 15.1° | 2.7 ft |
| 30% | 16.7° | 3.0 ft |
| 40% | 21.8° | 4.0 ft |
| 50% | 26.6° | 5.0 ft |
| 60% | 31.0° | 6.0 ft |
| 70% | 35.0° | 7.0 ft |
| 80% | 38.7° | 8.0 ft |
| 100% | 45.0° | 10.0 ft |
What the numbers mean for other mowers
You may be weighing a robot against a mower you push or ride. The University of Georgia's extension service gives two limits worth knowing:
- Riding mowers slide and roll over on slopes steeper than 27%. That is about a 2.7-foot drop over 10 feet.
- Push mowers can be used on slopes up to 20 degrees, which is about 36%.
The same page says to mow a slope with a push mower by working across it, side to side, starting at the bottom. With a riding mower you go up and down, and turn on level ground. Wet grass and loose soil change everything, and no chart accounts for them.
Robot mowers on the market are rated well above both of those limits. One review site's list runs from 45% to 84%. See the ones confirmed so far.
Put your number into the yard checker
Sources: University of Georgia Cooperative Extension, Forsyth County, read November 4, 2026. Degree and percent conversions are arithmetic (percent = tangent of the angle × 100).