Robot mower slope ratings, explained

The short answer

• Percent isn't degrees. A 100% slope is 45°, not vertical. A "45%" mower handles about 24°.
• There are two limits. Many makers publish a maximum slope inside the lawn and a much lower limit at the boundary, often 10% to 25%.
• Wet grass costs traction. Navimow's own guidance says wheels slip on wet grass and recommends mowing in dry weather.
• Measure first. A string, a line level and a tape measure are enough.

Percent vs degrees

Slope percent is rise over run: how many units the ground climbs for every 100 units you walk across it. Husqvarna gives the same formula in its installation guide: vertical height divided by horizontal distance, times 100. A lawn that rises 15 cm over 100 cm is a 15% slope.

Degrees measure the angle instead. The two don't scale together: 100% means the ground rises as much as it runs, which is 45°. To convert, degrees = arctan(percent ÷ 100).

The number that usually matters more: the edge limit

A mower can climb more steeply in the middle of a lawn than along its edge, where it has to turn and follow the boundary without sliding off it. Many makers publish this as a separate, lower number:

• Husqvarna says standard Automower models manage 25–50% depending on the model, and AWD models such as the 435X AWD up to 70%. Its 410iQ/420iQ/440iQ manual allows 45% slopes but a maximum of 15% for the boundary wire. Husqvarna's advice: if your lawn's edge is steeper than the limit, move the boundary further in.
• Segway Navimow lists a "Maximum Slope Ability" and a separate "Maximum Slope Performance at Boundary" on its spec pages. Its H-series manual says not to mow areas steeper than 45% and to keep the edge under 10%.
• Mammotion advertises 80% (38.6°) for the LUBA 2 AWD and Worx 84% (40°) for its Vision Cloud 4WD. Neither product page we read gives a boundary figure or attaches conditions to those numbers.

So for a sloped yard, check the edge limit against your steepest edge, not just the headline number against your steepest hill.

Wet grass and real-world grip

Slope ratings are maximums. Navimow's own help article says wet grass is slippery and the wheels slip, and its manual recommends mowing in dry weather for the best results. If your slopes are near the rating, expect a mower to struggle after rain or early in the morning with dew. Leave margin: a mower rated 45% for a 40% bank is cutting it close.

How to measure your own slope

With string and a line level

1. Push a stake into the ground at the top of the slope and another a few feet downhill.
2. Tie a string to the top stake at ground level and run it to the lower stake.
3. Hang a line level (a few dollars at a hardware store) on the string and slide the string up or down the lower stake until the bubble is centered.
4. Measure the horizontal length of string between the stakes (the run), then the height from the string down to the ground at the lower stake (the rise).
5. Slope percent = rise ÷ run × 100. A rise of 12 inches over a run of 40 inches is 30%.

This is the method New York City's Department of Environmental Protection teaches in its slope-measuring lesson.

With a phone

Apple's Measure app has a built-in level that shows the angle in degrees, and many Android phones have similar apps. Lay a straight board on the slope, set the phone on it, read the angle, and convert it with the table above. Measure the steepest part, and measure along every edge where the boundary will run.

What this means when you buy

• Pick a mower whose inside rating beats your steepest hill with some margin, and whose edge rating beats your steepest edge.
• If one bank is far steeper than the rest, it may be cheaper to exclude it than to buy an AWD mower for one patch.
• Our mow-my-lawn guide lists each mower's slope rating, and the System Builder only offers a mower for a sloped yard when its maker's rating is on record.

Related: how robot mowers navigate · robot mower safety.

Sources

• Husqvarna: optimising an Automower installation for steep slopes (Feb 2026)
• Husqvarna Automower 410iQ/420iQ/440iQ operator's manual
• Navimow spec page
• Navimow Academy: what to do if your Navimow slips on slopes (Aug 2026)
• Navimow H-series user manual v2.1
• Mammotion LUBA 2 AWD product page
• Worx Landroid Vision Cloud 4WD product page
• NYC DEP: measuring slope lesson
• Apple: use the level on iPhone

All sources read October 12, 2026. Slope ratings are the makers' own figures.