Short answer: Many robot mowers are built for hills, and makers claim a wide range, from gentle slopes to very steep ones. Measure the steepest part of your lawn in percent, compare it to the maker's claimed maximum, and leave a safety margin, because the claim is a best case, not a promise for every lawn.
Figures in this article come from our catalog of 378 robot lawn mowers (data as of 2026-10-07). They are what the makers claim.
What does slope percent mean?
Slope percent is how many units the ground rises for every 100 units you walk across flat ground. A 25% slope rises 25 cm (or 25 feet) over 100 cm (or 100 feet) of distance. That is rise over run, times 100.
Makers use percent, but many people think in degrees. Here is how they line up:
- 10% is about 6 degrees
- 25% is about 14 degrees
- 35% is about 19 degrees
- 45% is about 24 degrees
- 50% is about 27 degrees
- 80% is about 39 degrees
- 100% is exactly 45 degrees
Percent grows faster than degrees. A 100% slope is not a "very steep 90 degree wall". It is a 45 degree hill, which is still steep for a lawn.
If a spec sheet gives degrees, convert it before you compare. A maker listing "20 degrees" is talking about a slope of roughly 36%.
How do I measure the slope of my lawn?
You do not need special tools. Use the steepest part of the area the mower will cover.
- Take a straight board about 2 meters (6 feet) long, and a level.
- Rest one end on the ground at the top of the slope. Hold the board pointing straight downhill, and raise or lower the other end until the level shows the board is horizontal.
- Measure the gap between the free end of the board and the ground below it. That is the drop, or rise.
- The board's length is the run (it is horizontal).
- Divide rise by run, and multiply by 100.
For example, a 50 cm gap under a 2 meter level board gives 25%.
If you prefer your phone, a free inclinometer app can show the angle. Most show degrees, so use the list above to convert. Hold the phone flat against a long straight board rather than directly on the grass, so small bumps do not skew the reading.
Measure in a few spots. Slopes on lawns are rarely even, and the steep patch near a retaining wall or a bank is the one that matters. Also note slopes that run sideways across the mower's path, not only straight up and down. Makers may treat these differently, so check the manual.
What slopes do makers claim?
Among the 349 models with a claimed maximum slope in our data:
| Claimed maximum slope | Models |
|---|---|
| 25-34% | 50 |
| 35-44% | 73 |
| 45-54% | 137 |
| 55-79% | 26 |
| 80% or more | 63 |
The middle of the range is 45% (about 24 degrees). A quarter of the models claim 40% or less, and a quarter claim 55% or more. The lowest claim is 25% (about 14 degrees) and the highest is 100% (45 degrees).
So if your steepest patch is 30%, most models claim to handle it on paper. If it is 60% or more, your list gets shorter: 89 models (26 plus 63) claim 55% or more.
Why is the claim only a maximum?
A claimed slope is the steepest incline the maker says the mower can climb. It does not say the mower will do that every day, in all weather, on every kind of ground.
Several things can reduce what a mower manages in real life:
- Wet grass. Wet blades and wet soil are slippery. Wheels spin more easily.
- Loose or bare ground. Soft soil, mulch, gravel, and bare patches give the wheels less to grip.
- Long or thick grass. More drag for the wheels and more load on the motor.
- Rough surfaces. Bumps, ruts, and tree roots can tip a mower or lift a wheel.
Wheel slip can also leave marks on a lawn, especially when the mower turns on a slope. Makers often write extra limits in the manual, such as a lower slope for the edges of the lawn or for turning. Check the manual for any such limits, and for what the maker says about slopes near ponds, roads, or drops.
A sensible habit: pick a mower whose claimed slope sits comfortably above your steepest spot, rather than right at it.
Are there mowers with extra grip on hills?
Yes. Some models drive all wheels, not just two, and some use larger or more aggressively patterned wheels. Makers present these as helping on hills. Our catalog does not record drive type, so we cannot give counts here. If slope is your main worry, look for the drive layout and wheel design in the specs, and ask what the maker says about wet grass.
What this means for you
- Measure your steepest spot in percent and write it down.
- Treat the maker's maximum as a ceiling, not a target.
- Be more careful if your hill is wet, shaded, bare, or has loose soil.
- Supervise the first runs. Read the safety section of the manual before you start.
For the details-minded
Claimed maximum slope varies by navigation type in our data. Models that rely on a boundary wire have a median claim of 35% among those with a figure. For models using RTK (satellite positioning with a correction signal) plus cameras, the median is 45% and the upper quarter claims 80%. Models using 3D LiDAR plus cameras have a median of 50%. These are claims, and the test conditions are usually not stated. Sources differ, so one model may show different slope figures on a maker page and a retailer page. When you shortlist, check the manual itself.
Quick answers
Is 25% slope steep? It is about 14 degrees, which most people feel as a noticeable hill when walking. It is the lowest claim in our data.
Is a 100% slope the same as 90 degrees? No. 100% means the ground rises as much as it runs, which is exactly 45 degrees.
Should I trust the maker's slope number? Treat it as a claim from the maker. Leave a margin, and read the manual for conditions and limits.
What if part of my lawn is too steep? Some people leave that part to a trimmer or a push mower, or mark it as a no-go zone if the mower supports it. Check the manual.
Next step
Not sure what your lawn needs? Try the quiz to narrow down models by slope and size. For measuring your whole yard, see how to measure your lawn. For a full list of what to look for, see how to choose a robot lawn mower. Wet weather matters on slopes, so also read do robot mowers work in rain and winter.