"Robot Mowers on Slopes: How to Measure Your Yard's Grade"
Updated 2026-09-27
Every robot mower lists a maximum slope, and it's one of the easiest specs to get wrong. A mower that can't handle your steepest patch will spin its wheels, skip that area or get stuck. Here's how to read the ratings and check your yard.
Percent vs degrees
Brands quote slope in percent, degrees, or both, and the two are not the same. Percent is rise over run: a 45% slope climbs 45 inches for every 100 inches across. A 100% slope is a 45° angle, not a vertical wall.
| Slope rating | Angle | What it looks like |
|---|---|---|
| 30% | 17° | A gentle bank; most lawns are flatter than this |
| 45% | 24° | A noticeable hill you'd lean into walking up |
| 50% | 27° | Steep enough that push-mowing it is hard work |
| 80% | 39° | A very steep bank; hard to stand on when wet |
| 100% | 45° | Near the limit of what's safe to walk on |
When a brand gives only degrees, you can convert: percent = tan(angle) × 100.
How to measure your steepest spot
You only need the steepest section the mower will have to drive, not the average across the yard.
- Phone method: lay a straight board (4 ft or longer) on the slope, pointing straight downhill, and set your phone on it. The Level tool in the iPhone Measure app, or any free inclinometer app on Android, reads the angle in degrees. Convert with the table above.
- Level and tape method: rest one end of a 4 ft level on the slope, pointing downhill, and lift the low end until the bubble is centered. Measure the gap under the low end in inches. Slope % = gap ÷ 48 × 100. A 12-inch gap is 25%; a 24-inch gap is 50%.
Measure in two or three places, including any bank next to a driveway, path or flower bed, and use the highest number.
Leave headroom
Slope ratings are maximums under good conditions. Wet grass, loose soil or a slope that also tilts sideways all reduce grip, and climbing uses more battery, so a mower working near its limit may cover less per charge. As a rule of thumb, pick a mower rated comfortably above your steepest measurement rather than right at it. Also check the manual: some brands allow less slope along the boundary or on a side-slope than straight up and down.
What the ratings look like in our data
- Up to 30%: entry models such as the Navimow i105 and the Worx Landroid Vision range. Fine for gently sloped or flat lawns.
- 45–50%: most two-wheel-drive, wire-free mowers, including the Navimow H2 and X3, ANTHBOT Genie and ECOVACS GOAT models. Enough for typical suburban lawns with a few banks.
- 80% and up: all-wheel-drive mowers from Mammotion, Dreame and Navimow (X4 series, 84%), plus the tracked Lymow One Plus (100%). See best robot mowers for steep slopes for the full list.
All-wheel drive matters more than any other feature on hills: it's the main difference between the 45–50% group and the 80% group.
Next steps
Once you know your slope, the yard matcher filters mowers by lawn size, slope and tree cover together. If your yard has several separate areas as well as hills, read robot mowers for lawns with multiple zones, and how to measure your lawn for the area side of the equation.