How long does it take to mow an acre?

Every mower listing tells you deck width and most tell you a speed. Almost none multiply the two, which is a shame, because that multiplication is the only thing that answers the question people actually have: how much of my Saturday does this take?

The formula

Two of the three inputs are published. Deck width always is. Ground speed sometimes is — EGO publishes 0.9 to 3.1 MPH for the LM2135SP's self-propel drive and 8 MPH top speed for the Z6. Overlap never is, because it is a property of how you mow rather than of the machine.

The arithmetic, worked in full

A factor of three, from one machine to another, on the same acre. That is the entire argument for a rider, expressed in the only currency that matters on a big lot.

Minutes per acre, by deck and speed

Treat the 8 MPH row as a ceiling rather than a plan. Top speed on a zero turn is a transport figure; cutting at that speed on real grass would mean a poor cut and uncomfortable ride. The 4 MPH row is the one to budget against.

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The allowances nobody builds in

Swath times speed describes an infinite open field. Actual lots are not that, and the difference is not small.

• Turns. Every pass ends in a turn where you are covering no new ground. On short runs this is a large fraction of the time; on long runs it is negligible. Deck width does not help you here, run length does.
• Obstacles. Trees, beds, posts and play equipment all force slower passes and extra trimming afterwards.
• Trimming. Everything the deck could not reach is a second job with a second tool. On a heavily bordered lot that can rival the mowing time.
• Bagging. Every stop to empty is time, and it scales with how much grass you are removing rather than with area.
• Battery swaps and charging. Which is the other half of this problem entirely — see acres per charge, which works out the energy rather than the time.

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Cross-checking time against energy

The nice thing about having both calculations is that they can be checked against each other. Take the 21 inch self-propelled figure of about 126 minutes per acre and put it next to the published energy rates.

That disagreement is worth showing rather than hiding. It is a reminder that both numbers rest on assumptions somebody made, and that ours are at least written down where you can change them.

#ad Check the EGO Power+ 21" Select Cut LM2135SP price on Amazon — how we're funded.

Five ways to actually cut the time

1. Mow longer runs. Orienting passes along the long axis of the lot removes turns, and turns are pure overhead.
2. Overlap less, deliberately. Going from 15% overlap to 10% on a 21 inch deck is roughly a 6% time saving for the whole job.
3. Mow more often, not longer. The extension guidance to remove no more than a third of the leaf tissue means an overgrown lawn needs slower passes or two cuts.
4. Mulch instead of bagging where the growth allows it. Every emptying stop is time that is not mowing.
5. Buy deck width before you buy speed. Doubling the deck halves the time; adding 0.5 MPH to a walking pace does not.

What we cannot tell you

We have not timed any of these machines on any lawn. The overlap allowance and the walking and cutting speeds are our assumptions, stated so you can substitute your own. No manufacturer publishes a minutes-per-acre figure, and any site that gives you one without showing this arithmetic has made it up.

What the arithmetic does give you is a defensible starting number and a way to see which lever matters. On this evidence it is deck width, and it is not close.