Watts to PS - Garden Machinery and Small Engine Power

Lining Up a Mower's Watt Rating With a Petrol Engine's PS

Garden machinery sits awkwardly between two worlds. The electric mower on the shelf is labelled 1 800 W, the petrol one beside it claims 3 PS, and the shop assistant will happily tell you they are "about the same". Converting one into the other takes seconds — but the far more useful part is understanding what each number was measured on before you trust the comparison.

Conversion factor: 1 W = 0.001359621617 PS, so divide by 735.49875. A 1 800 W corded rotary mower comes out at 2.45 PS, which looks close to a 2.99 PS petrol machine until you check where each figure is taken.

What Each Rating Is Actually Measuring

Corded tools print what they draw

The watt figure on an electric mower or hedge trimmer is input power from the socket. Motor losses, fan drag and gearing mean rather less than that reaches the blade.

Petrol engines print shaft output

A small engine's PS is net power at the crankshaft at a stated speed, measured to a test standard. It is already an output figure, so it is not directly comparable with an input watt rating.

Battery machines quote volts

A cordless range is sold on 18 V, 36 V or 80 V because the platform matters more commercially than the output. Volts alone say nothing about power without the current.

Cutting width sets the workload

A wide deck or a long bar demands more power for the same grass or timber, so the rating only means something alongside the size of the cut it has to drive.

Working Through a Garden Machinery Spec Sheet

Most shed-buying decisions come down to comparing three or four boxes with three or four different labels. This is the order that keeps it honest.

Enter the electric machine's watts

Type the rating from the box or the rating plate — 600, 1 400, 2 000. The PS equivalent appears as you type, and spaces inside the number are ignored so 1 800 pastes straight in.

Put the petrol figure beside it

Now you have both machines in PS. Treat the electric value as generous, because it started life as input power while the engine's number is measured at the shaft.

Reverse it for a petrol-only listing

Second-hand adverts often give PS and nothing else. Press the swap button (↔) to run PS → W: a 5 PS tiller engine is 3 677 W, which puts it on the same scale as everything electric you have looked at.

Keep the numbers for the comparison

The copy button hands over the bare figure with no unit attached, ready for a notes app or a spreadsheet column. Ctrl + C inside a field does the same.

Input and output are not the same quantity: converting 1 800 W of mains draw into 2.45 PS is arithmetically exact, but that PS figure is what the machine consumes, not what it delivers to the blade.

Garden and Small Power Equipment in Watts and PS

Typical ratings across a domestic shed, converted exactly, with a note on what each manufacturer's figure is taken from. The last column is the one that decides whether two rows can fairly be compared.

Machine	Rated power (W)	Equivalent (PS)	What the rating means
Corded hedge trimmer	600 W	0.82 PS	Mains input
Cordless mower, 36 V	1 000 W	1.36 PS	Brushless motor output
Corded rotary mower	1 400 W	1.90 PS	Mains input
Electric chainsaw	2 000 W	2.72 PS	Mains input
Petrol mower, 140 cm³	2 200 W	2.99 PS	Net shaft power at rated speed
Petrol chainsaw, 50 cm³	2 600 W	3.54 PS	Net shaft power at rated speed
Corded blower-vacuum	3 000 W	4.08 PS	Mains input
Petrol tiller, 200 cm³	3 700 W	5.03 PS	Net shaft power at rated speed

Read down the last column and the marketing trick becomes obvious. The 3 000 W blower converts to a headline 4.08 PS, larger than the 2.99 PS petrol mower, yet almost all of that is air drag and heat rather than useful work. The cordless mower's 1 000 W is quoted at the motor output and is worth considerably more than the same number would be on a mains label.

Useful While You Are Comparing Machines

Run a whole shed in one sitting

Both fields are editable and follow each other live, so you can type over the previous machine's rating and keep going without clearing anything.

Send a petrol figure the other way

Reversing the direction turns an engine's advertised horsepower back into watts, which is the only way to line it up with a shelf full of electric labels.

Handle boxes that print kilowatts

Professional saws and tillers are often rated in kW rather than watts. The searchable dropdowns carry the whole power range, so no separate step is needed.

Small fractions stay readable

A 600 W trimmer lands well under one PS, and results carry up to eight decimals so a fraction of a horsepower is still a meaningful number.

What Buyers Ask About Mower and Chainsaw Ratings

Is an 1 800 W electric mower as strong as a 2.5 PS petrol one?

On paper they look level: 1 800 W converts to 2.45 PS. In the grass they are not, because the electric figure is what the machine pulls from the socket while the petrol figure is what the crankshaft gives out. Strip the motor and drive losses out of the electric rating and rather less arrives at the blade. As a rough guide, treat a corded mower as competitive with a petrol machine of noticeably smaller stated power.

Does the wattage on a corded tool mean power at the cutting head?

No — it is consumption, the number that matters for the fuse and the cable. Some of it becomes heat in the windings, some drives the cooling fan, some is lost in the gears. Where a maker does quote output it will say so on the plate, and that value will be clearly lower than the input for the same machine.

Why do battery machines advertise 40 V or 80 V instead of watts?

Voltage identifies the battery platform, which is what keeps a customer buying the same brand's tools. It is not a power figure: power is volts multiplied by current, so a 40 V machine drawing 25 A is 1 000 W, or 1.36 PS, while another 40 V tool drawing 10 A is well under half that. If you want to compare cordless machines meaningfully, look for a stated output in watts and the battery's amp-hours for run time.

Which matters more on a chainsaw, the PS figure or the bar length?

They have to match. A long bar buried in hardwood asks for more power to keep chain speed up, so fitting an oversized bar to a modest saw just makes it bog down and wear the clutch. Manufacturers state a maximum recommended bar for each output; a 2 600 W (3.54 PS) saw is comfortable on a mid-length bar, while a 2 000 W electric one belongs on a shorter one. Chain sharpness changes the felt difference more than either number does.

Why does my mower bog down in wet grass if the rating looks high?

Ratings are quoted at a machine's happiest operating point, not while it is dragging a wet mat of clippings. Damp grass multiplies the load on the blade, the motor or engine slows, and on an electric mower the current climbs until the thermal cut-out steps in. Raising the cut height, slowing your walking pace and cutting when the lawn is dry does more than swapping to a machine with a bigger figure on the box.

Watts to Metric Horsepower