Draw the lawn as shapes: add the outline you mow, then take away the house, the drive, the patio and the beds. You get the grass you actually mow, in square feet and acres, what two mower makers say suits that size — they do not agree — and how long each mow takes.
Your lawn, after taking away 1,500 sq ft
8,100 sq ftThat is 0.19 acres of grass to mow.
- Lawn
- 8,100 sq ft
- In acres
- 0.19 acres
- Outline
- 9,600 sq ft
- Taken away
- 1,500 sq ft
- Mowing time, Exmark’s rule of thumb
- 22 min with a 21-inch deck
What the makers say suits it
- Exmark (a Toro company): A walk-behind mower.
“Most lawn mower buying guides use a ¼-acre of actual mowing area as the walk mower threshold.” Exmark — What Size Mower is Right for Your Lawn? · checked 2026-09-25
- Cub Cadet: A reel mower, or a push or self-propelled mower.
“Reel mowers are great for homeowners that have less than one-fourth of an acre. A push or self-propelled mower is ideal for yards less than a half-acre.” Cub Cadet — The Ultimate Lawn Mower Buying Guide · checked 2026-09-25
The time is Exmark’s own estimate — a 42-inch deck mows about an acre an hour — scaled to your deck. Trees, beds and slopes make it longer; type your own pace for your own answer.
Maker guidance checked 2026-09-25.
Quick answer: measure the outline of the grass you mow, multiply length by width, then subtract the house, the drive, the patio and the beds. Divide by 43,560 for acres. A lot’s size is not the grass you mow: take out the house and the drive and the number drops — and that number, not the lot size, is the one to buy a mower for.
How to use it
Add the lawn as one or more shapes — a rectangle for the main stretch, a triangle for the corner by the fence, a circle for the island round the tree. Then add rows that take away: the footprint of the house, the drive, the beds, the pool. Each row can be feet or metres, or an area you already know (“300 sq ft”, “0.2 acre”). The answer is the grass you actually push or drive over, in square feet and acres.
Pick your deck width and the tool gives a mowing time from Exmark’s own rule of thumb — a 42-inch deck on a garden tractor mows about an acre an hour — scaled to your deck. If you know your real pace, open “Your own pace and fuel” and type it, with the overlap you leave between passes; that answer is yours, not a maker’s. Type how long a tank lasts you and it says how many mows you get per fill.
Which mower suits it — and why the makers disagree
Two makers publish guidance, and they do not draw the same lines:
- Exmark puts the walk-behind limit at a quarter acre of actual mowing area; from a quarter acre to an acre, a riding mower with a deck under 40 inches (or a 30-inch self-propelled walk-behind); a 42-inch deck for an acre to an acre and a half; 42 to 48 inches up to three acres; wider beyond that only on flat, open ground.
- Cub Cadet says a walk-behind “should do just fine” under an acre: push or self-propelled below half an acre, a wide-area walk-behind (23 to 33 inches) or a 30-inch mini rider from half an acre to an acre, and a lawn tractor or zero-turn from an acre up.
Between a quarter acre and an acre, then, one maker says ride and the other says walk. Both are right about different lawns. A flat, open quarter acre is an easy walk; a hilly one full of trees and beds is a long afternoon. Both makers also say the same thing about width: the wider the deck, the faster the open ground goes and the harder the corners and gates get. Measure your narrowest gate before you fall for a 54-inch deck. We have written about this at length for particular sizes: 42 or 46 inch, what size mower for 1.5 acres, and what counts as a medium-sized lawn.
Measuring without a tape
Pace it. Walk ten ordinary steps along a tape or a known length once, divide, and you have your own pace in feet; then pace the lawn and multiply. It is accurate enough for buying a mower or ordering seed. For odd shapes, split them: a rectangle for the bulk and a triangle for the wedge is closer than one rectangle that pretends the wedge is square. A kidney-shaped bed can be a circle; an L-shaped lawn is two rectangles.
Why the time is only a guide
Exmark’s acre-an-hour is an estimate for a garden tractor on an ordinary lawn. It already allows for turning and overlap, which is why it is slower than any mower’s top speed. Every tree you circle, every bed you trim round and every slope you take slowly adds to it. The honest version is the one you type yourself: time one mow, or type your speed and overlap and let the tool do the division.
What it does not do
It does not measure from a map. The free public aerial imagery for the US — the USGS National Map — is cached only down to about 2.4 metres a pixel, too coarse to trace a garden lawn honestly, so this page asks for the shapes instead. It does not size a mower by horsepower either; engines are a separate question from deck width.