Lawn mower horsepower – the power output of a gas powered lawn mower engine – is an important consideration when you are trying to choose the right lawn mower for your needs.
Understanding lawn mower engine power is not straightforward because manufacturers state engine power using different measures. These are usually horsepower, kilowatts, torque, or cubic capacity. They also publish power outputs based on different conditions. For example, power may be stated with the engine turning at various revolutions per minute, or ‘net’ or ‘gross’ according to whether with accessory parts are attached. When comparing lawn mower engine power, it is therefore vital to make sure you compare like with like. This article will show you how to do that.
Power output matters because it directly affects the performance, fuel efficiency, and the ability of the mower to handle various lawn conditions.
Put simply, a more powerful engine delivers more power to the critical moving parts – the drive wheels, and the cutting blades (or just the blades on a push mower).
What this means in practice is that a lawn mower with more power capacity can work more effectively than a lower powered mower on tougher terrain, e.g., significantly sloping ground, or uneven, bumpy surfaces. A higher-powered mower can also cut through rough, overgrown lawns and longer grass more effectively than a lower powered mower.
You should bear in mind that the amount of power delivered to the wheels and blades is not only determined by the engine output. It also depends on how efficiently power is delivered to these parts, and that depends upon the quality and efficiency of the mower’s overall design and construction.
However, engine power is the most important factor you need to understand if you want to know if a mower will have the ‘muscle’ for the kinds of conditions you need it for.
As we noted in this post about how to choose a gas powered lawn mower, it is critical think about the size of the areas you need to mow and the kind of ground you’ll be mowing on when you’re determining how powerful your lawn mower needs to be. Consider the size of the lawn, whether you have slopes to deal with, rough or uneven ground, long or lush grass or grass that is mown infrequently. If you have any of those conditions, you’ll need more power.
Lawn mower engine power for different conditions
I’ve set out below under each measure of power some suggested levels of power that you will generally need for the following different kinds of conditions:
- Small gardens: less than 1/4 acre, flat ground, no major obstacles, regularly mown;
- Medium gardens: 1/4 to 1/2 acre, some slopes, some rougher terrain, less frequent mowing;
- Large gardens: More than half an acre, obstacles, slopes, less frequent mowing
Note, these are broad guidelines, not hard and fast rules. Your conditions will likely be a bit different from the ‘typical’ conditions that I have used for these definitions, and more likely will fall somewhere on the scale between definitions.
You may also just want a machine with more or less power based on budget or personal preference. So you will need to adjust your thinking accordingly.
Lawn mower engine power: how to decipher what the manufacturers tell us
I’ll start this section by saying that I’m no mechanic or engineer. But I am long standing gardener and lawn mower user, and in this post I feature images from two of the lawn mowers I have owned:
- a John Deere self propelled mower powered by a 190cc 700 series Briggs and Stratton engine and
- a Honda HRU mower powered by a 163cc Honda GXC160 engine.
I also have a background as a practicing lawyer and a Master of Science degree. So, although I’m not technically qualified in mechanics or engineering, I’ve owned mowers powered by engines from the leading engine manufacturers, and I know how to research and sift information and data and how to present it in a way that is comprehensible to non-technicians.
And, when it comes to lawn mower engine power, that is pretty important.
This is because there are several different ways that power can be measure and expressed and it is hard to make comparisons across these different measures. It is especially so, because the lawn mower engine manufactures tend to present the data in different ways.
So with that said, let’s look at how you might see the power of lawn mower engines described when you are looking for the best gas powered lawn mower for your needs.
Horsepower
Horsepower (hp) is one of the units of measurement used to express the power output of a lawn mower engine (or any engine, for that matter). Historically, this is probably the most widely used way of expressing power output. It dates back to the 18th Century, when James Watt invented the steam engine. He worked out the power output of draft horses in order to compare ‘horse power’ with the steam power of his new engine.
There are different standards of horsepower including imperial and metric versions which differ slightly. But when comparing manufacturers’ information about lawn mower horsepower, it is probably most important to differentiate between two particular types of horsepower: gross horsepower and net horsepower.
Gross Horsepower vs Net Horsepower
Gross horsepower is the total power produced by an engine without taking into account any losses of power due to associated parts, such as an exhaust system or an air filter.
In contrast, net horsepower refers to the actual power output of the engine available for work when accounting for those losses. Net horsepower is therefore often lower than gross horsepower because of the power losses caused by the extra parts.
For example, a lawn mower engine might have a gross horsepower of 6.5 hp, but if it were measured in net horsepower, it might be closer to 6.0 hp.
Net horsepower is a better indication of the power that will actually be available for driving the mower in practice.
How much lawn mower horsepower do you need for your conditions?
- Small lawn:
- A push mower would usually be okay for this type of lawn. These kinds of mowers are fairly lightweight and the engine does not drive the wheels. Therefore, an engine delivering between about 2.5 and 4.5 horsepower will suffice.
- Medium lawns:
- A self-propelled mower with a 4.5 to 7 horsepower will probably do the job on a medium lawn.
- Large lawns :
- Here is when you are starting to get into the territory of riding mowers, zero-turn mowers and lawn tractors. You’ll need an increasing level of power with every acre you need to cut, e.g., 12 to 14 horsepower for 1/2 acre up to 24 horsepower plus for 3 acres or more.
Cubic capacity
Cubic capacity, also known as engine displacement, is measured in cubic centimetres (cc) or litres (L). It represents a measurement of the total volume of all the engine cylinders.
Technically, the cubic capacity of a cylinder is a measure of the total volume of air and fuel that is displaced by the piston as it rises up through the cylinder. If the engine has more that one cylinder (as riding mowers may do) the cubic capacity of both cylinders is added together to give the the total size of the engine.
Therefore, cubic capacity is not a measurement of engine power. Rather it indicates the size of the chambers central to the internal combustion process of the engine.
There is is no direct relationship between horsepower and cubic capacity because there may be other aspects of the way an engine is made that affect the power output. In other words, two engines with the same cubic capacity may produce different horsepower outputs.
But, all other things being equal, larger volume cylinders will produce more power. For example, a a 190cc lawn mower engine will likely have more power than 140cc one.
What size lawn mower engine in cc do you need for your conditions?
- Small lawns :
- A push mower with a 125cc to 140cc engine.
- Medium lawns:
- A self-propelled mower with a 140cc to 200cc engine.
- Large lawns:
- You’ll need a riding mower, zero-turn mower and lawn tractor. The smallest of these have engines around 350cc, the largest have engines up to 750cc.
Kilowatts
Kilowatts (KW) is another unit of measurement for power output, similar to horsepower. It is the accepted unit of power under the International System of Units. You will often see it referred to as the SI unit and tends to be used more by European or Asian lawn mower engine makers, such as Honda.
To convert horsepower to kilowatts and vice versa, you can use the following formula conversions:
- 1 hp = 0.7355 KW
- 1 KW = 1.3596 HP
Thus, an engine producing 5hp output, produces 5 x 0.7355 = 3.68 KW
This conversion might be necessary when comparing lawn mower engines from different manufacturers, as some may list power output in kilowatts and not in horsepower.
How much lawn mower power in KW do you need for your conditions?
- Small lawn:
- A push mower delivering between about 1.8KW and 3.3KW of power.
- Medium lawns:
- A self-propelled mower with a 3.3KW to 5.2KW engine.
- Large lawns :
- Riding mowers, zero-turn mower or lawn tractor with increasing level of power with every acre you need to cut, e.g., 8KW to 10KW for 1/2 acre up to 18Kw to 20KW plus for 3 acres or more.
Torque
Torque is the rotational force that an engine produces and applies to the drive shaft. In cars, torque is an indicator of speed of acceleration. In lawn mower engines, it is also related to the spinning of the blades and, therefore, their effective cutting power.
Torque is usually measured in pound-feet (lb-ft) or Newton-metres (Nm). A higher torque value indicates a more powerful engine capable of working under tougher conditions, such as cutting through thick grass and tackling inclines.
For example, a lawn mower engine with a torque of 7.5 lb-ft might perform better in cutting long thick grass than one with a torque value of 6.0 lb-ft.
How much lawn mower torque do you need for your conditions?
- Small lawn:
- A push mower delivering between about 6.1 Nm (4.5 lb-ft) of torque.
- Medium lawns:
- A self-propelled mower with a 7.46 Nm (5.5 lb-ft) to 10.00 Nm (7.36 lb-ft) of torque.
- Large lawns :
- Riding mowers, zero-turn mower or lawn tractor with increasing level of power with every acre you need to cut, e.g., 24 Nm (17.0 ft·lb) of torque at 2,500 rpm for 1/2 acre in a 350cc engine up to 50 Nm (36.88 ft-lb) plus for 3 acres or more in a 750cc engine.
Rpms
Revolutions per minute are not a measure of power output. But they are relevant here because figures given by manufacturers for horsepower, Kws or torque are usually, but not always, published on the basis that the engine is running at a given number of rpms. Usually, but not always, this is 2,500 or 3,600 rpms.
Comparison of lawn mower engine power
With this information you should be better placed to make comparisons between the different engines that are used in the lawn mowers you might be interested in purchasing.
Obviously, it is useful to see the information side by side. But sometimes it is not possible to make direct comparisons because:
- Some manufactures use net horsepower and some use gross horsepower. There is no direct formula for conversion from one measure to the other because the difference depends upon the additional parts and accessories that give rise to a net horsepower measure;
- Manufactures don’t all publish the same information: some publish figures for horsepower and torque, some publish in KWs and torque, some publish cubic capacity and horsepower, and so on;
- Power ratings may be given in the same units but at different rpms.
Nevertheless, as a general guide, here is what a comparison of different types of engine might look like:
| Engine | Cubic Capacity (cc) | Gross Horsepower (GHP) | Net Horsepower (NHP) | Kilowatts (kW) | Kilowatts (kW) |
|---|---|---|---|---|---|
| Small Gasoline Engine | 100-150 | 3-5 | 2-4 | 1.5-3 | 4-7.0 |
| Medium Gasoline Engine | 150-250 | 5-7 | 4-6 | 3.2-6.7 | 7.0-13 |
| Large Gasoline Engine | 250+ | 7+ | 6+ | 6.7.4+ | 13+ |
The two manufactures that make the vast majority of lawn mower engines are Honda and Briggs and Stratton. So below we’ll cover off the power ratings for some of their most popular engines
Honda lawn mower engine power
Here are the power ratings published by Honda for their popular lawn mower engines:
| Engine Model | Power Output (kW/hp) Net @3600 rpm | Torque (Nm/lb-ft) Net @2500 rpm | Cubic Capacity (cc) |
|---|---|---|---|
| Honda GXV160 | 3.2 kW (4.3 hp) | 9.6 Nm (7.1 lb-ft) | 163 Cc |
| Honda GCV160 | 3.3 KW (4.4 Hp) | 9.4 Nm (6.9 Lb-Ft) | 160 Cc |
| Honda GCV190 | 3.8 KW (5.1 Hp) | 11.3 Nm (8.3 Lb-Ft) | 187 Cc |
| Honda GX340 | 10.7 hp (8.0 kW) | 26.4 Nm (19.5 lb-ft) | 389 cc |
Briggs and Stratton lawn mower engine power
Here are the power ratings published by Briggs and Stratton for some of their popular lawn mower engines:
| Engine Model | Power Output (kW/hp) Net @3600 rpm | Torque (Nm/lb-ft) Net @2500 rpm | Cubic Capacity (cc) |
|---|---|---|---|
| Briggs and Stratton 450E Series | Not available | 6.1 Nm (4.5 lb-ft) | 125 cc |
| Briggs and Stratton 550E Series | Not available | 7.46 Nm (5.5 Lb-Ft) | 140 cc |
| Briggs and Stratton 675EXi Series | Not available | 9.83 Nm (7.25 lb-ft) | 163 cc |
| Briggs and Stratton 875EXi Series | Not available | 11.87 Nm (8.75 Lb-Ft) | 190 cc |
| Briggs and Stratton 3000E Series | Not Available | 20.77 Nm (15.32 Lb-Ft) | 344 cc |
If you want to know what I think …
Obviously, the engine is only one part of the package when you are thinking of buying a lawn mower. You can check out the following post to help you choose the gas power lawn mower that is right for you:
And, by the way, if you want to know my opinion, based on my own experience, the Honda engine beat the Briggs and Stratton engine hands down.
Compared to the John Deere, Briggs and Stratton powered mower that I owned, the Honda mower runs much more smoothly, starts more reliably and is much less noisy. And all though it has a smaller engine (163cc vs 190cc) the Honda feels no less powerful.
Unless I had a small flat lawn, I’d choose a Honda mower every time:
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Last update on 2023-05-05 / Affiliate links / Images from Amazon Product Advertising API
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