Best robot mower for a small yard

Robot mowers are usually sold on how much lawn they can take. On a small lot the useful question is the opposite one: what is the least machine that will keep up? The published duty cycle answers it, and only one maker gives you both halves of that sum.

The short answer

The duty cycle is the whole spec

A robot mower does not need to finish the lawn in one run. It needs to get round often enough to keep the grass in trim, and that is set by how much of each day it spends cutting rather than charging.

An eighth of an acre is 5,445 sq ft. A machine cutting a 7.1 inch swath covers that in roughly 9,200 linear feet — under two miles — which a 40% duty cycle repeats comfortably. That is why the small machine is enough, and why paying for ten times the rated area buys nothing on this lawn.

The two, on published figures

1. Segway Navimow i105N — sized for the lawn, not the brochure

An eighth of an acre, 24 lb, 58 dB(A) and no wire to bury. On a small lot each of those matters more than it would on an acre: the machine is light enough to carry indoors for winter, quiet enough to run while people are in the garden, and installed without trenching a perimeter that is mostly flowerbed anyway.

It is also the only robot in our registry that publishes both run time and charge time, which is what makes the duty cycle above a computation rather than a guess.

The hard limits are published and worth respecting: 16 degrees of slope, an eighth of an acre, and a 7.1 inch cutting width that means many passes. Segway also publishes no minimum sky-view requirement for the RTK positioning, which is the open question under tree cover.

#ad Check the Segway Navimow i105N Robot Mower price on Amazon — how we're funded.

2. Husqvarna Automower 450XH — and why not to buy it here

An acre and a quarter, 270 minutes of mowing per charge, a 9.45 inch cut and GPS theft tracking. It is the most capable robot in our registry and the wrong answer for a small lawn.

The reasons are practical rather than snobbish. It needs a boundary wire round the whole perimeter — on a small lot that is a high ratio of wire to grass. Its boundary slope limit is 15%, which small urban lots frequently break at a driveway edge. And Husqvarna publishes no charge time, so you cannot work out how much of the day it will actually be cutting.

Where it belongs is the other end of the range — see robot mowers for one acre.

#ad Check the Husqvarna Automower 450XH price on Amazon — how we're funded.

Three checks before buying for a small lot

1. Measure the narrowest passage, not just the area. A robot that cannot get from the front lawn to the back will mow half your grass.
2. Check the steepest few feet. Sixteen degrees is a 29% grade, and a short bank at a driveway can exceed it.
3. Look up. Wire-free navigation is satellite-based, and Segway publishes no minimum sky view, so heavy canopy is a risk nobody has quantified.

The full pre-purchase list is in the robot mower checklist.

What we cannot tell you

We have not installed either machine. Segway publishes no battery capacity, no boundary slope limit and no sky-view requirement; Husqvarna publishes no charge time, no decibel figure and no cut height for the 450XH. Nobody publishes a minimum lawn size or a minimum passage width, which on a small lot is the specification that decides whether a robot works at all.