Can You Put a 20 Inch Blade On a 21 Inch Lawn Mower?

20 Inch Blade On a 21 Inch Lawn Mower

What do you do when your lawn mower is just a little too small for the job? You can’t very well go out and buy a new one – especially if you’re on a budget.

What can you do to make your old lawn mower work just a little bit better? One option is to put a bigger blade on it.

Very well, the lawn mower blades you use are at the heart of your mowing experience. So, can you put a 20 inch blade on a 21 inch lawn mower?

Does it actually work? And if it does, will it be safe to use? Keep reading to find out!

Can You Put a 20 Inch Blade On a 21 Inch Lawn Mower?

Yes, you can. However, it won’t be able to cut wide. So, I recommend using a 21-inch blade for a 21-inch mower deck. You should know your mower blade sizes so you don’t unnecessarily buy a non-fitting one. The size indicated on a lawn mower blade is directly related to the lawn mower’s deck size.

Related: Best file for sharpening lawn mower blades

Your mower’s deck size determines the size of the blades that you will need, and the decks are designed to accommodate specific blade lengths.

Fitting your mower with the wrong sized blades may cause many problems, such as leaving streaks of uncut grass if the blade is too short.

Do All Mower Blades Fit All Mowers?

The mower blade is a vital part of the lawn mower, without which it cannot function. Apart from the basic mower blade features, such as sharpness, compatibility of the blade with the mower is also crucial.

So, are mower blades universal, and can you interchange them between mowers? No, they are not universal and are, instead, mower-specific.

However, you can replace your blade with blades from a different manufacturer as long as they match the specifications provided by the mower manufacturer.

The features that must match are length, hole numbers, shapes, thickness, among others. For durability and efficient functioning, replacement mower blades should be a perfect fit.

Accurately identifying the type of blade that your lawn mower uses is the most crucial step in selecting another blade.

How to Identify the Type of Blade Used in a Lawn Mower

Below is an extensive guide on how you can do this.

Check the manufacturer’s manual

Checking the manufacturer’s manual is the easiest way to get information on your mower blade and details on how to replace it.

Determine the model and the make number

You can also identify blades using the model number. You will usually find the mower make and number on the chassis or deck.

You can input this information into Amazon to view a list of compatible blades. I recommend using genuine blades as they offer the best quality and fit.

Identify the blade part number

All mower blades have a part number that is stamped into their body. These numbers are usually unique to that part of the mower, and when searched on google, they will provide a list of sellers stocking it.

Unfortunately, this is not the most reliable method, as years of using the blade may have caused the blade to erode, making the number nearly impossible to read accurately.

Measure the mower blade’s dimensions

Measure the length, width, hole size, thickness, and other essential dimensions of your blade and use them to locate a replacement.

You can fall back on using its dimensions if you can’t use the other. Even better, you can carry your mower blade to a seller who will assist you in correctly identifying it.

Are All 21 Mower Blades the Same?

No, they are not. When purchasing a lawn mower, you must get an exact fit for your mower to avoid the problems that come with an ill-fitting blade.

You can tick several boxes to get the best fit for your mower: the blade’s dimensions, the owner’s manual, and the manufacturer’s care center or website.

Can I Put a Mulching Blade On My Mower?

Yes, you can. If you plan on mulching your lawn, mulching blades are a great way to achieve this without buying a new lawn mower.

However, you need to ensure that these blades are the right fit for your mower.

Here is how you can do that:

  • Measure the blade’s length diagonally between the cutting edges.
  • Measure the blade’s breadth and thickness.
  • Measure the diameter of the central hole, or if it comes in a different shape, note and measure its size.

Check and confirm that the blade you are buying fits these dimensions in your previous blades.

If you are hesitant, take the user manual with you when you go blade shopping and ask for help at the store.

Is Bagging Better than Mulching?

Bagging involves collecting the grass clippings for composting in a bin or disposal at an approved site.

On the other hand, mulching leaves the grass clippings on the soil surface in the yard for several purposes: releasing nutrients into the soil.

Let us compare these two methods on different factors to help you determine the best method to use on your lawn.

The equipment

You will need a quality mulching mower to mulch as effectively as possible. A mulching mower works to cut the grass clippings finely and pushes them to the ground to allow them to decompose faster.

To bag grass clippings, you need a mower with a bag attachment, a yard waste container that the trash company will collect, or a compost bin for making compost.

Visual appeal

The visual appeal of bagging and mulching is usually subjective, depending on your tastes and preferences.

Some people feel that bagging leaves the lawn cleaner and neater since all the grass clippings are removed, leaving no visible grass clumps.

Mulching, however, does not give the lawn a cleaner look due to the clippings left on the yard.

If you choose to mulch and want to improve the lawn’s appearance, we recommend that you mow the lawn frequently and cut only a third of the grass that has grown.

You can bag the longer clippings if the yard is overgrown to look neater.

Lawn health

Mulching is the best way to go if you want to improve your lawn’s health. When you mulch the grass clippings into the grass, they release nutrients into the soil over time and gradually increase its health.

If you choose to bag the clippings instead, you may need to consider chemical fertilizers to supplement your lawn’s nutrients.

Mulching the clippings into the lawn is a bit faster. When bagging, you will have the extra task of emptying and disposing of the bag’s contents after you are done mowing.

However, the spare time taken by bagging is not that significant. The best method for you depends on which factors are more important.

Can You Use a Mulching Blade On a Side Discharge Mower?

Yes, you can! The mulching blade on the lawn mower will result in the clippings being cut into much smaller pieces.

You can choose to sweep up the clippings later or leave them on the lawn for improvement. If you decide to leave the grass clippings to mulch, you need to control where the grass clippings go.

You can do this by mowing a strip, reversing the direction, and trimming the next strip so that the clippings go where you had previously cut.

Do New Mower Blades Need to Be Sharpened?

No, they do not. Lawnmower blades are usually sharpened during manufacturing, and you can use them immediately after you buy them.

However, if you have already used the blades, you will need to sharpen them regularly to keep them working effectively.

When dealing with mowing blades, the standard rule is to sharpen them after approximately 25 hours of use, although this depends on the frequency with which you mow the lawn.

Apart from monitoring run time, you can also tell when you need to sharpen your blades by how they are cut.

If you notice that after you mow, the lawn is cut unevenly or several missed spots, it is time to sharpen the blades.

Read: How to sharpen riding mower blades without removing them?

It is also crucial to know when you can no longer sharpen your blades and need to replace them, which we discuss in detail below.

What’s the Difference Between High-Lift Blades and Mulching Blades?

Several types of mower blades are designed for different purposes. Two of the most common ones are high-lift blades and mulching blades.

Below we take a critical look at these two types, what they do, and how they differ.

Mulching blades

Mulching blades are also widely referred to as all-purpose blades. This blade has a curved surface that helps it work in three primary ways: mulching, lifting, and mowing.

The mower blade works by first pulling the grass up and cutting it, then pulling the grass clippings into the deck, where there are finely chopped.

The clippings are then blown out through air pressure created by the blade’s inner curve.

Mulching blades are the best choice for anyone who wants a blade that can also mulch the clippings back to the ground to replenish them.

The mulching blade also has cutting edges to cut grass more finely before discharging it onto the earth.

Since the blades have extra curves on the outer and inner surfaces, the clipped grass moves to the deck, where it is cut even more finely as the inner curves allow the particles to settle into the ground.

  • They are versatile as you can use them simultaneously for three different purposes.
  • The curves on the blades help to cut the grass into smaller pieces.
  • Mulched grasses help in improving lawn health by releasing nutrients to the soil.
  • Not very good for side discharge and bagging.
  • The deck can get clogged when used on overgrown lawns.

High-lift blades

High-lift blades are mower blades designed for lawns with tall, wet grass that require a high horsepower engine for mowing.

They are easily distinguishable from the vertical angles on the edges, allowing maximum airflow and providing these blades with the most significant suction power out of all lifting blades.

This suction ensures that no grass accumulates in the chute, leading to blockages.

High-lift blades also give an almost perfect trim as the speedy circular motion of the blades keeps the grass taut, allowing you to cut with greater precision.

It is also a great choice of blade for mowers for whom bagging is a priority.

  • The high suction and airflow prevent clogging when cutting tall, compact grasses.
  • They cut the grass neatly and give the lawn a more uniform and elegant finish.
  • They are an excellent choice for mowers who prioritize the bagging function.
  • High-lift blades do not perform so well on sandy terrains as the blades tend to pull in the sand too.
  • The high horsepower requirement may reduce the lifespan of your mower.

The Differences Between High Lift and Mulching Blade

Below we outline the main differences between high-lift and mulching blades.


Mulching blades, as mentioned above, have a curved design with two distinct cutting planes on the blade’s edge.

On the other hand, high-lift blades have a greater angle to the ground, with the angles on the corners creating the illusion of a thigh lift.

Working mechanism

Mulching blades create fine grass clippings that are uniformly redistributed back to the lawn to provide nutrients.

The grass is cut, and the clippings are recut into smaller pieces and finally forced into the ground for faster breakdown.

The mulching blade not only cuts grass but also discharges and mulches it. On the other hand, high-lift blades lift the grass clippings and help guide them with a discharge into the detachable bag.


The vertical edges on the high-lift blades help provide them with maximum airflow and excellent suction.

In mulching mowers, there is a re-circulating airflow as some of the air that goes into the cutting deck areas is also used to create air pressure that forces them into the ground.

Power Requirements

High-lift blades have a significantly higher power requirement and are best suited for mowers with a high power capacity.

These blades will not work best when paired with a mower that cannot supply the needed power.

On the contrary, mulching blades are better suited to mowers with lower power capacity since their airflow is reintroduced back into the system.

Other blade types are worth considering besides the mulching and high-lift mower blades. They include:

Other Lifting Blades

Lifting blades create an upward, vertical airflow that lifts the grass to provide a cleaner result.

Apart from the high lift blades discussed above, other lifting blades include the low-lift and medium-lift blades.

The low-lift blade

These blades are less curved on their edges and have low suction power. Because of the low suction, low-lift blades are best for working on sandy terrain as the dust won’t lift with the grass.

It also allows the grass to remain grounded enough for trimming and a side discharge.

As these blades require lower power, they also have the added advantage of being more durable than high-lift blades.


  • They need less horsepower hence do not strain the mower’s engine.
  • You can use them in sandy terrain.
  • Longer lifespan.
  • The curved ends keep the air pressure low, allowing the grass clipping to be discharged.


  • They do not suck the clippings into the bagging.

Medium-lift blades

These blades are commonly used in standard lawnmowers, with features between high and low-lift blades.

They have a slight curve on their ends that allows for a decent amount of airflow, creating suction that will enable you to pull up the grass for precise cuts.

You will often find these blades on mowers with a side discharge for the grass clippings.

While the high efficiency of these blades might make them a go-to choice for most gardeners, we recommend using them if your yard has thick grass patches and not light grass throughout.


  • They work well with different soil types.
  • Works well with both wet and dry grass.
  • The curved edges create adequate suction.


  • You may clog the chute if you cut too much grass.
  • They are not as effective on small clumps of grass low to the ground.

Gator blades

Gator blades combine low, medium, and high-lift features into a single blade, such as the serrated edges on both ends of the blade, allowing all-around cutting.

Like mulching blades, gator blades also work well to fertilize the soil. In a mulching blade, the angle of the teeth acts as a secondary blade that pulls the grass up to get the grass cut more precisely.

In a gator blade, the angle of the teeth moves the grass to the cutting edge as the mower moves.

The smaller grass clippings are then repeatedly cut to get them even smaller. You can also choose to equip the blade with a mulching kit to redistribute the grass clippings evenly to the ground.

  • The teeth on the blade direct the grass towards the sharp edge, resulting in a neater cut.
  • An excellent choice for mulching the clippings.

Cylinder blades

Cylinder mowers have a rotating cylinder fitted with blades and a stationary bed knife.

They are designed to cut grass that is not too long; otherwise, they will be overwhelmed and not cut as effectively.

The key to using mowers with cylinder blades is to cut the grass before it gets too long and alternate the mowing direction with alternative cuts, allowing for cleaner and more precise cuts.

Tips on Maintaining a Cylinder Mower

  • Regularly check if the mower is cutting properly by testing to see if the reel will cut paper strips. Also, ensure that the reel is not tight against the bed knife and touching.
  • Get a professional to grind the reel every two seasons as they wear down after some time.
  • Clean the mower after a few mows to keep the blades clean.

Why Does My Lawn Mower Cut Better Backwards?

There are several explanations for why your lawnmower may be working better when in reverse that vary with the type of mower you use.

In gas-powered mowers, the blades continue spinning in the same direction in reverse as they would when the mower is in the forward gear.

Non-powered push mowers have interlocking blades that are turned by the forward motion of the mower. When in reverse, the blades also turn in reverse.

Below are some reasons why your mower could be cutting better backward and our recommendations.

1. The deck height settings

This feature is probably the most common explanation for mowers that work better in reverse.

Ideally, the front end of the lawn mower should be slightly lower than the back end. The optimal deck pitch varies depending on the lawn mower that you are using.

To make adjustments, you can start with a pitch of around a quarter-inch and continue adjusting until you get to the desired setting.

2. Tire pressure

This factor directly ties into the deck height settings since the difference between the tire pressures of the mowers can affect their pitch.

If the back tires have less pressure, the blades will be closer to the ground on the back end, making the blades likely to cut the grass better in reverse.

3. The amount of cut grass

A standard rule when mowing is never to take off more than a third of the total length of the grass in your yard.

The cutting efficiency may decrease if the rear wheel goes over long grass and folds it beneath the deck.

Due to this, it can seem like your mower is working better in reverse since it has fewer obstacles at the rear to push and fold.

3. Clogging

A riding mower may perform better in reverse because of debris build-up in the front end that keeps the blades from functioning efficiently.

You can fix this by removing all the trapped debris and thoroughly cleaning the mower’s deck and the blades.

How Often Should You Change the Blade On Your Lawn Mower?

The frequency of replacing your lawn mower blades will depend on several factors.

Such factors are the type of grass on your lawn, the frequency with which you use your mower, the lawn size, and the general terrain of the land.

A standard rule is to replace the blades after approximately 100 to 200 hours of use. This time will vary depending on the actual condition of the blades.

Below are some of the things you should look out for when deciding to replace blades.

Visual inspection

The easiest way to tell if you need to replace your mower blade is to check its entire surface.

Debris, such as dirt and sand, can erode the blade over time and cause the blade’s material to become thinner and weaker.

If the blade looks dangerously weak, replace it as soon as possible, as it may break and injure someone. Also, ensure that you look for any large chips or dents you cannot sharpen.


The blades are probably dull if you notice any unevenness across the yard. When mowing is done with a mower blade in perfect condition, the cut will be even across the entire lawn.

You can get away with just sharpening the blade if it is just the regular dullness. However, if the blade is too damaged, you will need to replace it.

Mowing quality

You will also spot a blade that you need to replace by how it cuts the grass. Instead of cutting the grass cleanly and precisely, a dull or damaged blade will tear up the lawn.

This tearing will lead to damaged grass health, and if it is severe enough, it may lead to the grass turning brown and becoming unsightly.

Here are tips on how to take care of the mower blades to increase their lifespan.


  • Check the lawn for any sticks, stones, or other objects that may damage the blades before you mow. If you allow the blades to contact potentially dangerous things sooner, they will need sharpening more often and require replacement earlier.
  • Sharpen the blade in time. Sharpening the blade when needed will leave less damage to the blade’s edges.
  • Sharpen the blade correctly. Many blades need replacement much earlier because of improper sharpening techniques.

Using the wrong method may wear off some of the material from the blade’s edge and reduce the lifespan.

Final Thoughts

The blade size of the lawn mower is quite crucial and determines aspects such as how well it cuts and the amount of time it takes to mow your lawn.

Choosing the right blade size will save you time and effort and prevent any likely injuries to yourself or the machine. Still, the question remains…

Can You Put a 20 Inch Blade On a 21 Inch Lawn Mower

Yes, you can. However, I recommend using a 21 inch blade on a mower with a 21 inch deck size.

As mentioned above, if the blade is too short, it could leave several streaks of grass uncut as you mow.

Thank you for reading this article to the end, and I hope you found it helpful. Please leave any suggestions, comments, and queries you have in our comment section below.

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