string trimmer rpm

How Fast Does a String Trimmer Spin?

A string trimmer is a surprisingly powerful garden tool and some can spin incredibly fast, whereas others are much slower. In truth, the speed of the weed wacker will depend on various factors. Many people wonder about the string trimmer rpm, let’s take an in-depth look.

A string trimmer is a garden tool designed to cut back long weeds and grasses in places where the lawn mower would struggle to reach. They are often used around the edges of the lawn as well as behind flower beds and in other hard to reach places.

There are gas-powered weed eater tools as well as the electric weed eater, with the former being substantially more powerful. That being said, an electric trimmer is typically more lightweight, easier to use and requires little to no maintenance. Regardless of the power type, these tools feature a string wire or line that rotates at a high speed, therefore cutting through the foliage cleanly and quickly.

In the case of the gas-powered weed eater, a combustion engine is used to power the tool and this will typically deliver a higher speed. Fuel and air combine within the combustion chamber and a spark plug creates an ignition source, ultimately causing the engine to start. 

How Fast Does a String Trimmer Spin?

The weed wacker rpm will vary greatly depending on the individual tool. There are also several other factors that will affect it including the length of the string and the power of the motor. In most cases, a gas string trimmers RPM will be much faster than that of an electric model purely because these are more powerful engines by design. Even though some of the best electric string trimmers are now coming very close to rivalling the power of the gas models.

The average weed eater rotation is typically around 7000rpm but there are some tools that have a much slower rpm, with the minimum being around 3000rpm. That being said, you will also find many more powerful weed eater engine RPMs that soar up to around 15,000.

Calculating the speed of a weed eater engine involves a little bit of mathematics and it is important to keep in mind that the RPM near the end of the string trimmer wire will be less than that of the inner part of the wire. Depending on the length of the string, this could vary quite significantly.

In addition to this, you must think about the speed when the weed eater propeller is in idle mode compared to what it is when the tool is at full speed. Let’s explore this in a little more detail.

Idle Speed

When running in idle, most string trimmers will have an RPM of between 2700 and 3000 but this will vary by model. For example, the Stihl weed wackers tend to have an idle speed of 2800RPM.

High Speed

When you are running your weed eater at a much higher speed, the RPM can increase significantly. On average, you would expect to see at least 7000RPM but as we have already mentioned, some of the more powerful string trimmers may have an RPM up to 15,000.

We looked at the idle speed of the Stihl weed eater and once this garden tool is put into high speed mode, you can expect it to have an RPM of around 10,500. It is not difficult to see that there is a significant difference between the two modes.

String Length

Regardless of whether your weed eater is idling or at full throttle, the length of the string will have an incredible effect on the RPM. This is because a longer string is not physically able to spin as quickly as a shorter string. However, if your string is too short, it isn’t going to cut effectively.

There is a lot of information surrounding the correct length of a string trimmer wire but much of this can be very detailed. We wanted to break this down to help you understand the importance of getting the trimmer line length spot on before restringing your weed eater.

Some people will remove the trimmer guard as a way of installing a much longer weed eater line. However, this comes with many risks including flying debris and a lower RPM. So, while you may be able to cover more ground at any given time, the lesser speed may mean that you have to go over the same area more than once meaning that this method likely won’t benefit you.

The reason that a longer string will affect the RPM is that the engine is having to work harder to move more string. There is a limit to what any engine can do and this means that there has to be a compromise somewhere. In this case, the lengthier wire comes at the expense of speed.

Gas String Trimmer RPM

A gas string trimmer is comparatively more powerful than an electric. This is not something that can be changed even if some of the recent electric models are coming close to their gas counterparts.

The RPMs we have discussed so far typically relate to a gas string trimmer with speeds running between 3000 at an idle level through to 10,000-15,000 when running at high speed. However, it is also important to consider the type of gas weed eater engine. There are two types: the 4 stroke weed eater and the 2 cycle weed eater.

2 Stroke vs 4 Stroke

The key difference between a 2 stroke engine and a 4 stroke engine is the number of rotations required to complete a full engine cycle. There is a process that the weed eater engine needs to go through in order to create power.

When the weed eater cord is pulled, this begins the process which starts with the flywheel sending energy to the ignition which causes the spark plug to give off a spark, igniting the fuel and turning it to gas which in turn, makes the engine work. When the engine is running in idle, there is a clutch that spots the flywheel from rotating meaning that the engine doesn’t have power to run, resulting in the slower speed.

This process continues and repeats with each rotation of the flywheel, delivering a constant stream of power for the weed wacker to operate. When we consider a 2 cycle engine, the entire engine process is completed in two rotations, whereas a 4 cycle weed eater engine requires four rotations.

With all of this in mind, we have to assume that a 2 cycle weed eater engine would produce a far greater speed than its 4 cycle equivalent. Owing to the quicker cycle, a 2 stroke engine is generally considered to be more powerful. That being said, the torque of a 4 cycle engine is known to be much greater, not to mention that these engines are typically a lot more fuel efficient and greener to run.

Electric String Trimmer RPM

An electric string trimmer has many advantages. For example, these tools tend to be much more lightweight owing to the fact that they do not have weighty engines but a much more compact electric motor.

There are corded electric weed eaters and those that operate on battery power. What’s more, there is no complicated start up and with the simple push of a button, you’re powered and ready to go. However, the downside to these weed eaters is that they are not anywhere near as powerful as gas models.

That being said, modern electric weed wackers are easily able to achieve an average RPM between 6000 and 8500 which is more than sufficient for most domestic gardening applications. Furthermore, you will often find that an electric weed eater has the option to adjust the spin rate according to the type of foliage you are dealing with. However, if you are using a cordless model then it is important to keep in mind that the higher the RPM, the more quickly the battery will drain meaning you will need to wait for it to recharge. This is not an issue with gas trimmers as you can simply top up the fuel and move on.


A weed eater may be a slimline tool but the power it wields is seriously impressive. Some of these garden tools can move at an astonishing rate of 15,000RPM. At the lower end of the scale, when running in idle, you might expect the trimmer to spin at around 3000RPM. However, there are many factors that will affect this including the type of motor you are using and the length of the trimmer line.

Andrew Fisher

Andrew Fisher

Andrew is a dedicated father of three who really takes pride in his lawn and garden. You'll find Andrew behind the scenes of almost everything Edge Your Lawn produces. When he's not helping readers find all the information they need, he's in his backyard working on his lawn and garden landscaping. This year he hopes to build an outdoor deck and sort out his veg patches.

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