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Robot Mowers

Robot Mower Calculator: Coverage, Slope and Boundary Wire Length

Last updated Researched from specs, manuals and owner reviews, not tested in person

Quick answer

Choose a robot mower rated for about a third more area than your lawn, so it runs near 75 percent of capacity: a quarter-acre lawn of 10,890 square feet needs a model rated for about 14,500 square feet. Match the slope rating too, where 45 percent equals about 24 degrees, and budget roughly 1.1 feet of boundary wire per foot of edge for wired models.

Robot mowers are sold by maximum rated area and maximum slope, and both ratings assume a simple, open lawn mowed on the manufacturer's schedule. Enter your lawn area, steepest slope, how many separate zones and narrow passages it has, and its edge length, and the calculator recommends the minimum rated area, the slope rating you need, a boundary type and, for wired models, how much wire and how many stakes to buy. Measure first with the lawn size calculator if you need the square footage.

Robot mower calculator

Walk the edge or add up the sides.

Look for a rated area of at least

13,333 sq ft

Robot mowers that fit your lawn

Top matches update when you calculate.

On this page
  1. What size robot mower do I need for my lawn?
  2. How steep a slope can a robot mower handle?
  3. How does the robot mower calculator work?
  4. Do I need a wire-free robot mower?
  5. How long does a robot mower take to mow a lawn?

What size robot mower do I need for my lawn?

Minimum rated area at about 75 percent loading, with the two lowest-priced catalog models that meet it.

Robot mower rated area by lawn size
LawnSquare feetRated area to look forModels that fit
0.1 acres4,3565,808Segway Navimow i210 AWD Robot Mower, Segway Navimow i215 LiDAR Robot Mower
0.25 acres10,89014,520Segway Navimow i215 LiDAR Robot Mower, Husqvarna Automower 410iQ Robot Mower
0.5 acres21,78029,040Husqvarna Automower 420iQ Robot Mower, Mammotion LUBA 2 AWD 3000X Robot Mower
0.75 acres32,67043,560Husqvarna Automower 420iQ Robot Mower, Husqvarna Automower 440iQ Robot Mower
1 acre43,56058,080Husqvarna Automower 440iQ Robot Mower
1.5 acres65,34087,120Husqvarna Automower 440iQ Robot Mower
2 acres87,120116,160No catalog model; consider two mowers or a rider

How steep a slope can a robot mower handle?

Slope in degrees and percent
DegreesPercentRise over runCatalog robots rated for it
5 degrees9 percent1 ft rise in 11.1 ft10 of 12
10 degrees18 percent1 ft rise in 5.6 ft10 of 12
15 degrees27 percent1 ft rise in 3.7 ft10 of 12
20 degrees36 percent1 ft rise in 2.8 ft10 of 12
24.2 degrees45 percent1 ft rise in 2.2 ft10 of 12
30 degrees58 percent1 ft rise in 1.7 ft3 of 12
35 degrees70 percent1 ft rise in 1.4 ft3 of 12
38.7 degrees80 percent1 ft rise in 1.3 ft3 of 12

How does the robot mower calculator work?

It works in three steps:

  • Rated area needed = lawn area / 0.75, then increased by 10 percent for each extra zone beyond the first and 10 percent if the mower must travel through narrow passages to reach part of the lawn, because travel time is time not mowing.
  • Slope needed = your steepest slope in percent, converted from degrees if needed (percent = tangent of the angle x 100).
  • Boundary wire = (edge length + 25 feet for each tree, bed or obstacle you wire around + a guide wire about half the lawn's length) x 1.1 for slack and joins. Stakes are estimated at one every 2.5 feet, but follow the spacing in your mower's installation manual.

Wire-free models using RTK satellite positioning, cameras or LiDAR need no perimeter wire, but RTK units need a clear view of the sky for their reference station and can struggle under dense tree canopy, while vision models can struggle in poor light. That trade-off is covered in boundary wire vs RTK robot mowers.

Do I need a wire-free robot mower?

Wire-free is worth paying for when your lawn edges change often, when you have several zones you would otherwise wire and connect, or when you do not want to bury or stake several hundred feet of cable. The Segway Navimow i105N Robot Mower ($799.00) brings wire-free mowing to small lawns, the Mammotion LUBA 2 AWD 3000X Robot Mower combines RTK and vision with all-wheel drive for slopes, and the Husqvarna Automower 420iQ Robot Mower uses Husqvarna's EPOS satellite positioning. A wired model such as the Husqvarna Automower 430X Robot Mower costs less for its rated area and does not depend on satellite reception, which makes it a sound choice for simple lawns under heavy tree cover. Picks are ranked in robot mowers without boundary wire and robot mowers for hills.

How long does a robot mower take to mow a lawn?

Robot mowers do not mow in one session. They cut a little every day, usually in random or systematic passes at under 1 mph with a narrow blade disc, then return to charge. A mower loaded at 75 percent of its rating typically needs most of its scheduled daily hours to keep up in peak growing season, and less later in the year. That is why rated area matters more than blade width: a mower that is too small for the lawn simply falls behind and the grass gets away from it. Quiet electric operation means many owners run them overnight or while at work, but keep children and pets off the lawn while any robot mower is running.

Frequently asked questions

What size robot mower do I need for a half acre?

A half acre is 21,780 square feet, so look for a robot mower rated for at least about 29,000 square feet, which leaves roughly 25 percent headroom. Models rated for 0.75 acres or more fit comfortably. If the half acre is split into front and back zones connected by a narrow side yard, size up again, since the mower spends time traveling between areas instead of cutting.

How much boundary wire do I need for a robot mower?

Measure the lawn edge, add about 25 feet for each tree, bed or obstacle you loop the wire around, add a guide wire of roughly half the lawn length, and multiply by 1.1 for slack and splices. A simple 100 by 100 foot lawn with two islands needs about 550 feet. Most wired kits include 500 to 800 feet, and extra wire and stakes are sold separately.

Can a robot mower handle hills?

Yes, within its rated slope. Many two-wheel-drive models are rated around 35 to 45 percent, which is about 19 to 24 degrees, while all-wheel-drive models such as AWD Automowers, Mammotion Luba and Segway Navimow AWD are rated higher. Ratings apply to the steepest section, and wet grass reduces traction, so leave margin rather than running a mower at its limit.

Is a robot mower worth it for a small yard?

For lawns under a quarter acre, a robot mower is mostly a convenience purchase: a battery walk-behind costs less and mows the same area in about half an hour a week. Robots make the most sense where your time is scarce, mowing is physically difficult, or the lawn is large enough that daily automatic cutting saves hours. Their daily trimming also leaves a very even finish.

Do robot mowers work in the rain and at night?

Most robot mowers are weatherproofed and can mow in light rain, and many include rain sensors or app settings to pause mowing when wet, which protects the lawn and traction on slopes. Many can run at night, but owners and wildlife groups often recommend daytime schedules to avoid harming animals. Check your model manual for the recommended weather and scheduling settings.

Researched, not professional advice. This page is compiled from published specifications, manuals, labels and owner-review consensus, not hands-on testing. Follow the manufacturer's instructions and product label, and consult a qualified professional where safety, chemicals, fuel or structures are involved. As an Amazon Associate we earn from qualifying purchases.