Ryobi ONE+ Lawn Mower Guide: 18V Deck Sizes, Real Runtime and Who It Suits

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A Ryobi ONE+ lawn mower is an 18V cordless push mower that runs on the same batteries as Ryobi’s ONE+ drills, trimmers and blowers, and it makes the most sense for small lawns, roughly up to a quarter acre at the generous end, owned by someone who already has a few ONE+ packs. If your yard is bigger, your grass is thick, or you want self-propel, Ryobi’s 40V line is usually the better fit. Here is how the 18V mowers compare, what runtime to realistically expect, and where the edger fits in.

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First, a naming clarification: 18V, not 20V

Ryobi’s ONE+ system is 18 volts. Searches for a “Ryobi 20V lawn mower” usually come from the “20V MAX” labeling used by DeWalt, Craftsman and others, which is a peak-voltage figure for the same basic five-cell lithium pack. Ryobi labels by nominal voltage, so its 18V packs are electrically the same class as the “20V MAX” competition. There is no separate 20V Ryobi mower range; the choices are 18V ONE+ and 40V.

Likewise, the “33cm” ONE+ mower seen in UK and European listings is a 13-inch-class deck. North American ONE+ mowers have historically come in 13-inch and 16-inch deck sizes, with the larger ones in the ONE+ HP brushless family.

ONE+ 18V vs. Ryobi 40V mowers at a glance

The key line is watt-hours. An 18V 4 Ah pack holds about 72 Wh (18 x 4). That is the fuel tank, and it is small compared with a single 40V 6 Ah pack at 240 Wh.

Worked runtime estimate

A small brushless mower cutting average, dry, weekly-mowed grass commonly draws somewhere in the 300-500 W range, rising sharply in thick or wet grass. Using those figures:

• One 4 Ah ONE+ pack (72 Wh) at 400 W gives about 72 / 400 x 60 = roughly 11 minutes of blade time, a bit more with eco-style load sensing.
• Two 4 Ah packs (144 Wh) gives roughly 20-25 minutes.
• A typical walking pace with a 16-inch deck covers on the order of 4,000-5,000 sq ft in 20 minutes on an open, rectangular lawn.

Ryobi’s own runtime claims for the bigger ONE+ HP kits are longer than this, and on easy grass they can be met, but plan around the conservative number. If you already own several 4 Ah or larger ONE+ batteries, the practical answer is simple: keep a spare charged and swap mid-mow.

Who should buy a ONE+ mower

Practical strengths

• Shared batteries. The battery is the most expensive part of any cordless tool. Buying the bare mower when you already own packs can cut the cost substantially.
• Light and easy to store. Most fold their handles and can be stood upright or hung, which suits sheds and small garages.
• Low maintenance. No gas, oil, spark plug or carburetor. Seasonal care is blade sharpening, cleaning the deck and storing packs indoors.
• Quiet start. Push-button start, no pull cord.

Limitations to be honest about

• Narrow decks mean more passes. A 13-inch deck takes about 60% more passes than a 21-inch deck on the same lawn.
• Thick or wet grass drains packs fast. Raise the deck a notch, cut slower, and avoid mowing after rain.
• Bag capacity is small. Expect to empty the bag frequently in spring growth; mulching, where supported, helps.
• Older 1.5-2 Ah packs are a poor match. They will run a mower for only a few minutes and can overheat under the load. Use 4 Ah or larger, ideally the HP or high-output packs.

Getting the most out of 18V

1. Mow weekly in the growing season so you never remove more than one third of the blade height in a cut.
2. Keep the blade sharp. A dull blade raises power draw and tears the grass.
3. Scrape dried clippings off the underside of the deck; buildup increases drag on the motor.
4. Let batteries cool for a few minutes after mowing before charging, and store them indoors over winter at partial charge.
5. Mow the perimeter first, then run long straight strips to minimize slow turning time.

The ONE+ edger and other add-ons

Ryobi also sells an 18V ONE+ cordless edger for cutting clean lines along driveways and sidewalks. It uses a vertical blade, usually around 9 inches in diameter, and is far quicker for edging than turning a string trimmer on its side. It draws much less power than a mower, so a single 4 Ah pack covers the edges of a typical suburban lot. Pairing the mower, a ONE+ string trimmer and the edger on one battery platform is the main reason people choose the 18V mower in the first place.

Bottom line

The Ryobi ONE+ mower is a sensible, low-maintenance choice for small, regularly mowed lawns, especially if you already own ONE+ batteries. Run it on 4 Ah or larger packs, keep a spare charged, and keep the blade sharp. If the lawn is larger than about a quarter acre, sloped, or often overgrown, Ryobi’s 40V mowers give you three to five times the battery energy and are worth the extra money.