Most people start shopping for a robot mower by reading about mowers. It is worth doing the opposite first. A few measurements of your own yard will help narrow the field before you compare a single spec sheet, and they take about twenty minutes with a tape measure and a phone.
Here is what to collect, and what each fact does.
1. Mowable area
What to measure: the grass only. Not your lot size, not the driveway, not the flower beds. If your lawn is roughly rectangular, length × width is close enough. For an awkward shape, break it into two or three rectangles and add them up.
If measuring on foot feels tedious, trace the lawn in any satellite mapping tool that reports area, then subtract the beds.
Why it matters: every mower has a published coverage rating, and it is the bluntest filter available — a machine rated for a quarter acre is not a candidate for an acre.
One caution: coverage ratings are not all the same kind of number. Some are stated as a recommendation, some as a maximum, and some carry an explicit tolerance. Where a manufacturer attaches a qualifier to its own figure, we record it with the number:
If your lawn is near the top of a mower’s rating, treat the rating as the top.
2. Steepest slope in the lawn
What to measure: find the steepest patch of grass the mower will have to cross. Rest a straight board on the slope, level it, measure the gap under the downhill end, and divide by the board’s length. A 4-foot board with a 1-foot gap is 25%.
Why it matters: where a manufacturer publishes a slope rating, it is a hard limit. A mower rated below your measured slope is not a compromise — it is outside its stated envelope.
3. Slope at the edge of the lawn
What to measure: the same thing again, but where the grass ends — along the property line, beside the driveway, at the top of a retaining wall.
Why it matters: this is the measurement almost nobody takes, and it is often the one that rules a mower out. Some manufacturers publish substantially lower slope limits at the boundary than within the lawn.
How far the two slope ratings can diverge on the same machine
| Model | Inside the lawn | At the boundary |
|---|---|---|
| Husqvarna Automower 435 iQ AWD | 70% | 50% |
| Husqvarna Automower 435X AWD | 70% | 50% |
| Segway Navimow X330 | 50% | 25% |
| Segway Navimow X350 | 50% | 25% |
| Segway Navimow X390 | 50% | 25% |
| Husqvarna Automower 410 iQ | 45% | 15% |
| Husqvarna Automower 415X | 40% | 15% |
| Husqvarna Automower 440 iQ | 45% | 15% |
| Husqvarna Automower 450X EPOS | 45% | 15% |
| Segway Navimow i105 | 30% | 10% |
| Segway Navimow i110 | 30% | 10% |
Figures come from each manufacturer's own published material. Follow a model link for the exact source and the date it was last checked.
11 of the 19 models we track publish a separate boundary slope rating. Where it is not published, you will need to ask the seller directly.
There is more on both numbers in robot mower slope ratings.
4. How many separate areas
What to count: patches of grass the mower cannot drive between without crossing something that is not lawn — a front yard separated from the back by a driveway, a side strip behind a gate.
Why it matters: this is a question about what the mower can manage autonomously. A model without documented multi-zone support can still cut a second lawn if you carry it there and set it up, but it will not travel between areas or run them on one schedule by itself. If you want the whole property handled without your involvement, multi-zone support matters.
Published zone counts, on the other hand, are not something we can rely on:
0 of the 19 models we track publish a zone count we were able to verify.So treat this as a yes/no question about capability rather than counting on a specific number of zones.
Two things worth noting while you are outside
Where could positioning hardware go? Many wire-free mowers require a separate antenna or reference station with a clear view of the sky. Look for a plausible spot now, because it narrows the field considerably. See wire-free or buried wire.
How much tree cover is there? This matters most for systems that depend on satellite positioning, where obstruction can affect the fix. Systems that lean more on cameras or LiDAR are affected by different conditions. Manufacturers publish little that lets us compare models on this directly, so note it as a question to raise with the seller rather than a filter you can apply yourself.
What we cannot help you check
If your yard has a narrow gap the mower must drive through — a side gate, a path between a shed and a fence — measure it, but be aware of how little is published:
0 of the 19 models we track publish a minimum passage width.We will not estimate one from a machine’s body width, because a body width is not a clearance rating. Measure the gap and ask the seller directly before you commit.
Now use what you collected
Take your measurements to the mower selector. Alongside the yard facts above, it also asks two installation questions — whether you are willing to bury a perimeter wire, and whether you can install the antenna or reference station some models require — because those rule out models just as firmly as a slope rating does.
It applies each answer against verified manufacturer specifications, tells you plainly which models are ruled out and why, and flags the ones it could not check because the figure simply is not published.
If you come out with a shortlist, the comparison tool will put up to 4 models side by side — including the blanks, which are often the most useful part.