Robotic Lawn Mower Buying Guide

A robotic mower is one of the larger single purchases most people make for their garden, and it is unusually easy to get wrong. Not because the machines are bad — most modern ones work well — but because a mower that is excellent in one garden can be useless in the garden next door.

This guide goes through the decisions in the order that actually matters.

1. Start with the area, not the brand

The single most important number is the maximum working area the manufacturer publishes, in square metres. Everything else is secondary, because a mower rated below your lawn size will never finish a full cut, no matter how clever its navigation is.

Measure your lawn properly before you look at any product page. Pace out the length and width of each grassed section in metres and multiply them. Add the sections together. Leave out beds, paths, the patio and the driveway — the mower will not cut those.

Then allow some headroom. A mower rated exactly at your lawn area will be running at its maximum every single week, with no slack for a wet fortnight when the grass grows faster than usual. Around 20% more capacity than you strictly need is a comfortable margin.

2. Then measure the steepest slope

Slope is the most common cause of a robot mower failing in a real garden, and the one buyers most often underestimate.

Manufacturers publish a maximum gradient, usually as a percentage. A percentage is simply the rise divided by the run: a slope that climbs 30 cm over a metre is 30%. That is not the same as degrees, and the two are easy to confuse — 45% is roughly 24°, not 45°.

What matters is your steepest section, not the average. A mostly flat lawn with one steep bank at the bottom needs a mower rated for that bank. If the mower cannot climb it, it will slip, scalp the grass, and eventually get stuck there.

If the steep part is small and separable, an alternative is to exclude it from the mowing area altogether and trim it by hand a few times a year.

3. Look at the shape of the garden, not just the size

Two lawns of 800 m² can present completely different problems.

• Trees. Dense canopy interferes with satellite reception, which matters a great deal for mowers that navigate primarily by satellite.
• Narrow passages. A side path or gateway the mower must drive through needs precise positioning and a deck narrow enough to fit with clearance.
• Separate areas. A front and back lawn that do not join up need either multi-zone support, or you carrying the mower between them.
• Rough ground. Roots, dips and molehills are hard on drive systems. There is no published "roughness rating", so a strong slope rating is the closest available proxy.

4. Choose the navigation to fit the garden

This is where most of the marketing noise is, and where it pays to think about your own garden rather than which technology sounds most advanced.

• Boundary wire systems follow a perimeter cable you bury or peg around the lawn. It is old technology, cheap and extremely reliable — including under trees, where satellites struggle. The drawback is that changing the lawn layout later means moving the wire.
• Satellite positioning with RTK correction gives centimetre-level accuracy without any wire, and allows tidy, efficient mowing patterns. It needs a reasonably clear view of the sky, plus a correction signal — either from a network service over mobile data, or from a reference antenna you mount where it can see the sky.
• LiDAR builds a live map with a laser scanner, so it does not depend on the sky at all. It tends to appear on more expensive models.
• Camera vision recognises the lawn edge and obstacles visually. Performance varies with light and weather more than the other methods.

Many current models combine several of these. That is genuinely useful: a mower that can fall back on vision or LiDAR when the satellite signal drops under a tree will simply keep working, where a satellite-only model pauses.

5. Decide how much installation you are willing to do

Wire-free installation is a real convenience: you walk the mower around the boundary once, or draw it in an app, and you are done. Changing the layout later takes minutes.

A boundary wire takes an afternoon to lay properly, and stays put for years. It is also the only option that is completely unaffected by tree cover or tall buildings.

Neither is universally better. The right answer depends on whether your garden's biggest challenge is convenience or signal.

6. Check the practical details

These rarely decide a purchase on their own, but they decide how happy you are a year later:

• Cutting height range — matters if you like your lawn long or very short.
• Rain sensor — some models return to base in rain; some carry on. There are arguments both ways, but you should know which one you are buying.
• Anti-theft — a mower left out in an unfenced front garden is a visible target. PIN locks, alarms and location tracking are common.
• Connectivity — Wi-Fi is standard; cellular is useful for a garden out of Wi-Fi range.
• Warranty and support — check who handles a warranty claim in your country before you buy, not after something fails.

What to check before you buy

• Have you measured the lawn, rather than guessed?
• Have you measured the steepest slope, not the average one?
• Does the mower's published working area exceed your lawn with room to spare?
• Does its slope rating exceed your steepest section?
• If you have trees, does it have something other than satellites to navigate with?
• If you have separate lawns, does it genuinely support multiple zones?
• Is there a support route in your country if something goes wrong?

If you can answer all seven, you are unlikely to be disappointed. If you cannot answer the first two, nothing else on the list is worth thinking about yet.