How Sharp Should Mower Blades Be?

How Sharp Should Mower Blades Be

Lawnmowers must be sharp to cut grass easily and more effectively. Otherwise, you spend more energy mowing and risk ending with a poorly cut lawn that may hurt your curb appeal.

However, the common question is – how sharp should mower blades be? When can you confidently say you have a sharp lawn mower?

It’s not a very easy question. But we’ve gathered important tips and professional advice to help out.

How Sharp Should Mower Blades Be?

Lawnmower blades should be aggressively sharp but not razor-sharp. Generally, your mower’s blades should be sharp enough to cut the grass without tearing or ripping it. However, it shouldn’t be too thin to be easily damaged by debris and weeds in the lawn. Thus, we advocate for a butter-knife sharp but not razor-sharp blade.

Signs of a Dull Mower Blade?

Dull lawn mower blades present all sorts of problems. The following are common consequences of mowing with a dull blade;

  • Poor grass-cutting quality: The first problem with dull blades is poorly cut or shredded grass. It may cut the grass unevenly or may not cut some sections at all. So, you end up with a worse-looking lawn.
  • Loss of moisture: Shredding rather than cleanly clipping the grass when mowing significantly interferes with water transportation mechanisms in the grass blades, often signified by longer lawn healing times.
  • Severe discolouration (browning): Discoloration is one of the first signs of lawn moisture loss. The grass tips become brown, leading to brown patches throughout the lawn.  
  • Increased risk of lawn disease: Shredded, browning lawn grass increases the disease risk. For instance, dehydrated lawns often suffer leaf spots, a fungal infection that causes burn-like spots on the blades. Dollar spots and leaf blight are also common.
  • Reduced resistance to heat, drought, and pests: An unhealthy, dehydrated lawn is susceptible to drought, heat, and pests. Mulching may help. However, a few days of drought easily kills the grass.
  • Mowing inefficiency and faster wear/tear: You need more gas to cut grass with blunt blades. At the same time, the individual grass blades easily wrap around dull blades, increasing clogging rates. So, you spend more time unclogging the blades. It also puts more strain on the mower’s engine and transmission system, leading to faster wear and tear.

Should New Lawnmower Blades be Sharp?

Does new lawn mower blade need to be sharpened? This is a common question, especially among homeowners purchasing a new mower or replacing their mower blades for the first time.

Is it necessary to sharpen the new blade? The short answer is no. New mower blades are sufficiently sharp out of the box. So you can use them without sharpening them.

In fact, the blades are factory-sharpened, meaning they are perfectly sharp for lawn-mowing purposes.

Are new mower blades sharp when you buy them?

Yes, almost all new lawn mower blades are pre-sharpened at the factory. Therefore, you don’t need to sharpen them before the first use.

However, some new blades can feel dull. If so, contact the manufacturer for further information.

Why are new mower blades not sharp?

New mower blades may feel blunt due to a powder-coated paint finish along the edge.

Manufacturers apply the powder-coated finish to protect the blade from weather elements, especially rain and moisture. Doing so prevents rusting. It also slows down wear and tear.

The coating is particularly thick around the blade’s cutting edge, which can leave the blade feeling dull. However, the blades are often sharp enough for lawn-mowing purposes.

Should mulching blades be sharp?

Yes, mulching blades must be sharp as dull blades rip the grass, sometimes pulling some grass from the soil and ruining the lawn. Moreover, dull mulching blades invite rust and corrosion.

To this end, we recommend sharpening your mulching blades twice a season if you mow your lawn weekly or biweekly. Use a file and sharpen until the blade is butter-knife sharp.

How Sharp Should Lawn Mower Blades Be? 

Ideally, the mower blade should be sharp as a butter knife but not razor-sharp. It may seem wiser to have a sharper blade. However, overly-sharp blades are more susceptible to damage.

For instance, rolling (the folding over the blade edge) is a common challenge when the mower blades are too sharp.

Thinner blades are also more susceptible to damage from denting and tears from obstacles such as weeds and pebbles.

Related: Quick Tips for Sharpening Your Edger Blade

How to tell if the mower blade is sharp

  1. Visual Inspection: Examine the blade closely for signs of wear, nicks, or dents. A sharp blade will have a clean, smooth edge without visible damage.
  2. Paper Test: Hold a sheet of paper against the blade and try to cut it with a gentle slicing motion. A sharp blade should cut the paper effortlessly and cleanly.
  3. Blade Balance: Ensure the blade is properly balanced. A blade that is off-balance may cause excessive vibrations and uneven cutting.
  4. Blade Sharpness Indicators: Some mower blades have built-in indicators, such as color-coding or markings, to help you determine their sharpness.

How to Sharpen Mower Blades: A Step-by-Step Guide

The mower blade sharpening process varies slightly depending on the sharpening tool. Common sharpening tools include files, angle grinders, die grinders, and an electric drill.

Nevertheless, the following is a general guide on how to sharpen lawn mower blades.

  1. Wear safety equipment: Never sharpen mower blades without wearing protective gloves and safety goggles a the very least. It’s for your safety.
  2. Disconnect the mower: Remove the batteries using an electric mower or disconnect the spark plug wire using a gas or diesel mower. This precaution is to prevent accidentally switching on the mower during sharpening.
  3.  Drain the fuel tank (optional): This only applies to gas-powered push mowers. You must tilt a push mower on its side to access the blade. So, it’s only sensible to drain the fuel tank early to prevent gas leaks.
  4. Tilt the mower and mark the blade (optional): This step applies only to gas-powered push mowers. Tilt it gently on its side to access the blade, ensuring the carburetor and air filter remain upright to prevent fuel from flowing to the air filter. Then mark the blade, so you know which side faces up.
  5. Detach the blade: Many mowers have a long, threaded, hex-headed bolt attaching the blade to a blade adapter. Use a wrench to loosen this bolt. Then remove and keep the bolt safe. Also, you can take this opportunity to clean the grass clippings between the blade and adapter or cutting deck.
  6. Clean and inspect the mower blade: This is a good opportunity to decide whether to sharpen or replace the blade. If it’s too worn for lawn maintenance, replace it to keep operating costs down. However, if it’s in good condition, clean it with a penetrating cleaner and wipe it with a microfiber cloth. Then allow it to dry.
  7. Sharpen the blade: The exact sharpening process depends on whether you use a metal file, angle grinder, bench grinder, or a different sharpening tool. We’ll only explain how to sharpen your blade using a metal file or electric angle grinder. Clamp the blade using a bench vice and proceed as follows;
    • Sharpening lawn mower blade using a metal file: Find a 10-inch+ long file and hold it 45 degrees to its cutting edge. Then sharpen in one direction with a pushing motion. It takes less than 50 strokes to finish the job. Here’s a more detailed guide on how to sharpen lawn mower blades with a file.
    • Sharpening a lawn mower blade using an angle grinder: First, choose the right grinding wheel. A coarse wheel works best. So, find a 36-40 grit grinding disc. You can also use a flap disc. When ready, load the wheel onto the angle grinder and run it along the blade edge to sharpen, using lubricant to minimize heating. After finishing the first side, turn to the opposite blade edge.
  8. Ensure proper blade balance: A balanced blade is critical to efficient, cost-effective cutting and a quality lawn. Use a blade balancer to verify whether your blade is balanced.
  9. Finish up and reinstall the blade: Inspect it again to ensure it’s in good shape. If all’s well, mount it onto the deck and tighten the centre bolt.

Read: How to sharpen mower blades while still on mower?

Can a Lawn Mower Blade Be Too Sharp? How Sharp is Too Sharp?

Yes, lawnmower blades can be too sharp. Generally, the blade is too sharp if you’re terrified to run your finger along the edge.

Frequent rolling (roll-over) is another sign that the blade is too sharp. Beware that rollover can cause faster chipping and nicking.

How sharp should lawn mower blades be

How Often Should You Sharpen Lawn Mower Blades?

Many homeowners often ask how frequently mowers need to be sharpened. The best answer is to sharpen your lawn mower blades twice a year or every 25 hours.

You can also get away with sharpening the blade once yearly if you have a small lawn or your grass doesn’t grow very fast. If so, sharpen it once at the start of the mowing season.

However, don’t fall for the temptation to sharpen the mower blades every few days. Although it seems the right thing to do, sharpening blades too frequently wears the tool very fast.

Worse still, it keeps the blade too sharp, resulting in faster dulling and damage. The following are a few additional tips to help determine the right time to sharpen your mower blades. 

  • Inspect the glass: A sharp mower provides a straight cut. If your freshly mowed lawn is uneven or you notice torn edges, sharpen or replace the blade.
  • Terrain: Flat terrains with few rocks and impediments are perfect for mowing and kind on mower blades. So you don’t need to sharpen your blade’s edge frequently. Unfortunately, the opposite is true for rough terrain with pebbles, weeds, and other impediments.
  • Lawn size: Larger lawns necessitate more frequent blade sharpening. In this case, we recommend sticking to the once-every-25-hours sharpening rule.
  • Deck height: A lower deck height puts more obstacles in the mower blade’s way, causing faster dulling. Therefore, you need to sharpen the blade more frequently.

What Angle Should My Mower Blade Be?

The lawn mower’s blade angle is pre-set at the factory, typically between 30-35 degrees. Always maintain the original angle. For instance, set the blade to the same angle when sharpening.

Also, retain the 30-35 degree angle when reinstalling your mower blade. Tinkering with the factory-set angle can cause poor grass-cutting performance and faster blade wear.

Sharp lawn mower blade vs dull: Advantages of Sharp Mower Blades

  1. Sharp mower blades improve cutting efficiency by cleanly and evenly cutting through grass, reducing resistance and making mowing smoother and faster.
  2. They contribute to a healthier lawn appearance, creating a neater, more aesthetically pleasing look with uniform grass height.
  3. Sharp blades reduce strain on the mower’s engine, allowing it to operate more efficiently, prolonging its life, and saving on maintenance costs.


Should mower blades be razor sharp?

Mower blades should be sharp, but not razor sharp. Maintaining the right level of sharpness ensures efficient and safe cutting without damaging the grass or posing a risk of severe injuries.

Regular inspections and proper maintenance are essential for a healthier lawn and a safer mowing experience. Seek professional help if unsure.

Do replacement lawn mower blades come sharp?

Yes. All replacement lawn mower blades come pre-sharpened. They are factory-sharpened, so you can use them out of the box.

So, do not sharpen the new mower blade, as doing so can damage the blade and cause problems when cutting grass.

Is it better to sharpen or buy new mower blades?

It’s better to sharpen your blades than replace them until they are badly damaged or worn. Doing so allows you to maintain a healthy lawn while saving on blade replacement costs.

However, don’t hesitate to replace the blade when the time comes. Consult the manufacturer to learn the best replacement time.

Where can I get my lawn mower blades sharpened?

DIY sharpening is the best option. It lets you keep better track of blade performance and overall mowing efficiency.

However, commercial mower blade sharpening is another option. For instance, all ACE Hardware and NSL Saw & Tool stores offer mower blade sharpening services. Alternatively, google “lawn mower blade sharpening services near me” and see what comes up.

How much does it cost to sharpen lawn mower blades?

Push mower blade sharpening costs $5 to $15 per blade, depending on the blade type, size, and the sharpening service provider.

Expect to pay around $5 if you remove the blade and bring it for sharpening. Meanwhile, riding mower blade sharpening costs $20- $40. Again, it depends on blade size, type, and who detaches it.

See: Mulching blades for zero-turn mowers

Final verdict – how sharp should mower blades be?

Your lawn mower blade should be butter-knife sharp for optimal performance. A duller blade can damage the grass while putting unnecessary strain on the mower and rider/user.

On the other hand, razor-sharp mower blades dull easily and are prone to denting and chipping.