Automatic vs. Bump Feed Trimmer: Which is Better for You?

String trimmers make landscape grooming quick and easy. Also, they are a relatively more economical way of keeping your lawn or yard in good shape.

And although they come in various types and brands, one of the most important decisions that you have to make is whether to go for an automatic or bump feed trimmer.

While both types are powerful enough and will also cut grass efficiently, their mechanism of work is different. Each type will have some pros and cons and hence will be ideal for different kinds of users and situations.

Understanding these pros and cons and what sets the two common types of string feed systems apart should make it easy to pick the right one for you.

1. Automatic Feed Trimmer

Automatic Feed Trimmer

Whether you are grooming a large yard or do not have a lot of time to spare, you need a string trimmer that does the job fast and conveniently. And for most homeowners, the best option for this is an automatic feed string trimmer.

And as its name suggests, it is the kind that will advance the line automatically. With these machines, you do not have to stop to pull out more line or keep bumping the head on the surface to feed more line.

The mechanism on most automatic feed string trimmers will rely on centrifugal force to make the automatic line feed.

But, there are also some modern ones that have sensors that detect when the line is short and trigger a mechanism to feed more line. And the greatest advantage of these trimmers is that you never have to keep bumping or tapping the trimmer head.

Automatic feed string trimmers resemble the bump feed in many aspects from the shaft style to the mode of operation (corded or cordless) and so many people cannot tell the two apart just by looking at them.

However, the ability of the line on an automatic feed trimmer to advance without any intervention from the user is what set the two apart.

And because this trimmer will only draw more line when it reaches certain shortness, most of the time you will end up using less line than you would with a bump-feed trimmer.

The automatic line feed makes it possible to focus on the trimming or edging without having to worry about introducing more line to the machine. This can in turn help to speed up the task.

Line replacement is a little more expensive when using an automatic feed trimmer than a bump feed because most use pre-wound spools.


  • Continuous and uninterrupted operation. The automatic feed trimmer is by far the better option between the two when you want something that provides continuous and interrupted operation. With these machines, you never have to stop to tap the head to advance more line as it does this automatically and you will not even realize it. Hence you are free to focus more on the edging or trimming task at hand.
  • Uses less line. When using the bump feed trimmer you will get more line every time you tap the head even if there is still enough length on the head for efficient cutting. This can lead to a lot of waste. With an automatic feed trimmer, the line will only advance when it reaches a certain level of shortness and so you will always have just what you need for trimming to reduce wastage. In most cases, you will end up using less line than bump feed trimmer.


  • Entire spool replacement. The greatest shortcoming of most automatic feed trimmers is that they will require you to replace the entire spool when you need to add some new line to the machine. This can be quite expensive for many users. With the bump feed trimmers, you can remove the spool and conveniently rewind the line when it runs out.
  • Harder to maintain. While both types of trimmers are prone to jamming as a result of dirt and debris, the automatic feed ones have a more complicated system than the bump feed trimmers, and hence also harder to clear out the jam and maintain them.

2. Bump Feed Trimmer

Bump Feed Trimmer

You will often see people tapping or bumping their string trimmer against the ground when cutting grass. This might look strange if you have not used these machines in the past, but it is something vital for their performance.

The regular taps or bumps of the trimmer head against the ground are vital as they trigger the advancement of more line to maintain an efficient cutting head.

Unlike with the automatic feed trimmer, the line on a bump feed model will not advance forward until you trigger it to by bumping the head, and this is regardless of how short the exposed line might be.

The greatest advantage of the bump-feed is that it gives the users the freedom to get more line for cutting whenever they want it. And so it is possible to choose the amount of line to have on the head depending on the grass thickness or size.

Also, the bump feed trimmer is quicker than the automatic feed. However, this also means that it will use more line and hence add up to the cost of operating your string trimmer.

Since the line goes faster with a bump feed trimmer you will also have more downtimes when replacing it, and this is despite the fact that it is easier to change the line without having to replace entire spool.

Bumping your trimmer too much can also result in some issues such as wearing out of the spring that controls the release of the line and cracking the spool.

However, these trimmers will give you more control over the amount of line that you want to use when trimming or edging and they are generally easier to maintain than the automatic feed ones.


  • Simplified system. The bump feed trimmers have a more simplified system than the automatic feed machines and so they are relatively easier to fix in case they develop problems. Whether it is clearing a jam or changing a damaged spring it will be easy enough for most users to do on their own.
  • More control over the line. With the automatic feed trimmers, you do not have the ability to control how much trimmer line you use. But, the bump feed trimmers give you more control over the amount of line to use and so you can easily tune them to suit the application at hand. For example, you only need to tap the head more when you want a longer line for cutting thick brush.


  • Frequent stops. Unlike when using the automatic feed trimmers, you have to stop regularly to bump the head into something to feed more line. While this only takes a few seconds with most trimmer models, doing it regularly when cutting grass tends to slow down the task significantly.
  • More prone to damages. The constant bumps or tap makes the bump feed trimmers more prone to damages than the automatic feed machines. While many electric trimmer manufacturers are always devising new ways to minimize damages, the spring and spool are still quite prone to damage as a result of excess bumping that exposes the trimmer head to too much pressure.


Automatic Feed

Bump Feed

How it Works

  • Uses centrifugal force to feed more line automatically
  • Some also have sensors
  • Require a tap or bump onto a surface to feed more line.


  • Continuous and un-interrupted operation
  • Uses less line
  • Relatively easier maintenance
  • More control over the line


  • Requires replacement of entire spool
  • Harder to maintain
  • Uses more line
  • More prone to damage

Electric trimmers are one of the best tools for landscape grooming. And whether you choose to go for an automatic or bump feed model, you can be sure of getting something reliable for trimming and edging your yard and lawn.

However, what you pick between the two will always depend on your personal preferences and what you find most convenient.

An automatic feed trimmer is always the best option for those that like something that finishes the tasks faster with no delays as you never have to stop to bump or tap the trimmer head.

Also, the automatic feed is the better option when you want something that uses less line and hence requires fewer spool changes.

But, when you want to have more control over your line when trimming grass, the bump feed trimmer is your best pick.

Bump feed trimmers are also the best trimmer option for those that want something that is easy to maintain and also does not take a lot of effort or time to put in more line.

Ultimately, the choice between the two depends on your preferences and what you find most useful and convenient for your regular trimming needs.

Read More: 10 Best Trimmer Lines To Buy

Last Updated on February 23, 2019 by Tom Bradly

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Tom Bradly

My entrepreneurial journey started in 2006, when I dropped out of university. I wanted to work with my hands, to build things. Now I mix my background with computers with my first-hand experience with woodworking to provide insights into the tools I like best. I love everything about woodworking and have been building stuff for over 20 years of my life. I hope to pass some knowledge and expertise. See more at

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