The Complete Robot Lawn Mower Buying Guide

1. Coverage rating — and why you should discount it

Coverage is the headline number: the maximum lawn area the manufacturer says the mower can keep on top of. It's calculated from cutting width, speed and battery life, assuming the mower runs its full schedule on an open, dry, roughly rectangular lawn.

Your lawn is probably none of those things. A tree in the middle, a narrow passage to the back garden, a wet fortnight in spring — each one costs efficiency. The practical rule:

Measure your lawn, add 15%, and buy for that number.

Buying with headroom also means the mower finishes earlier, runs fewer hours per week, and the battery lasts more seasons. Buying right at the limit means it never quite catches up in peak growth, which is when people conclude the technology doesn't work.

How to measure

Trace the grass in any satellite mapping tool with an area function, or pace out the length and width and multiply. Break an irregular lawn into rectangles. Exclude beds, paths, the driveway and anything the mower will never touch.

2. Slope rating — read it as a hard limit

Slope is published as a percentage, not degrees, and the difference matters: 45% is about 24 degrees, not 45. A 100% slope would be 45 degrees.

Three things about the rating are worth knowing:

• It applies to dry grass. Wet grass can cut effective traction by a third.
• It applies to the steepest point, not the average. One short steep bank sets your requirement.
• It is not a target. If your steepest section is at the mower's rated limit, treat that model as out of range.

Two-wheel-drive mowers with a front caster are the standard design and typically top out between 25% and 45%. All-wheel-drive models exist specifically for properties that go beyond that. The slope guide covers this in more depth.

3. Navigation — three technologies, three trade-offs

This is the single biggest fork in the decision, and there is no universally correct answer.

Perimeter wire

A wire is pegged or buried around the lawn's edge. The mower detects the field and stays inside it. Installation is the slowest part of any robot mower purchase — a weekend of work, or a paid install — but once it's down it is completely indifferent to tree cover, cloud, tall buildings and satellite outages. Wire-guided mowers remain the most reliable option for shaded or complex gardens.

RTK satellite (wire-free)

A fixed antenna gives the mower centimetre-level positioning, and you draw the boundary in an app. Setup drops from a weekend to an afternoon and the mowing pattern is systematic — neat parallel passes rather than random bouncing. The catch is that RTK needs a clear view of the sky. Dense canopy, a tall hedge or a narrow side passage can all cause a lost fix.

Camera vision (wire-free)

The mower identifies grass visually and steers by what it sees. It doesn't care about satellite signal, which makes it the natural pick for heavily shaded lawns, and it can react to obstacles in real time. It's less precise on open ground than RTK, and it needs daylight.

A fuller comparison is in wire vs wire-free.

4. Runtime and charge time — the ratio, not the number

Runtime alone tells you little. What matters is the ratio of mowing time to charging time, because that determines how much of the day the mower is actually productive.

A mower that runs 60 minutes and charges 60 minutes works half the day. One that runs 180 minutes and charges 100 works nearly two thirds of it — and on a large lawn, that difference decides whether it keeps up in May.

On a small lawn the ratio is irrelevant: the mower finishes, docks, and waits. Only start caring about runtime above roughly a quarter of an acre.

5. The features that earn their place

• Rain sensor. Mowing wet grass makes a mess of the cut and packs clippings under the deck. Near-universal now, but check.
• Lift and tilt sensors. Blades stop when the mower is picked up or tipped. Non-negotiable with children or pets around.
• Obstacle avoidance. Genuinely useful if things get left on the lawn. Without it, the mower bumps and turns — fine for a tree, less fine for a garden hose.
• GPS tracking and a PIN. Worth having on anything expensive left outdoors.
• Multi-zone support. Essential if the lawn is split by a path or a gate.

And three that rarely do

• Voice assistant support. You will use it twice.
• Cut-height motorisation. Pleasant, but you set the height about twice a season.
• Ultra-high blade counts. Cut quality comes from sharp blades and frequent mowing, not blade count.

6. Noise — the spec that decides when you can run it

Robot mowers are quiet compared to a gas mower, but the range between models is wider than people expect: roughly 54 dB to 65 dB. That's not a small gap — decibels are logarithmic, so 64 dB is perceived as roughly twice as loud as 54 dB.

Under about 58 dB you can run the mower early morning or late evening without irritating anyone. Above 62 dB, in a garden with close neighbours, you're realistically limited to daytime hours — and that constrains how much mowing it can fit in.

What to actually spend

Robot mowers cluster into three bands, and the bands map to lawn types rather than to quality:

• Entry level. Small, simple, mostly flat lawns. Often wire-guided with basic navigation. Cut quality can still be excellent.
• Mid-range. Where wire-free navigation becomes affordable. The right band for most suburban gardens.
• Premium and above. Large properties, steep ground, or a genuine need for commercial-grade reliability and support.

Spending more does not buy a better cut. It buys coverage, gradient capability, navigation sophistication and support. If your lawn is small and flat, the entry band is not a compromise.

Ready to narrow it down? The lawn matcher filters the database on these limits automatically.