How to sharpen a lawn mower blade

It’s easy to tell when the blade on your push lawn mower is dull: the tips of the grass blades are tattered and brown. If the dull blade is in good shape otherwise, you can sharpen the mower blade yourself by following these instructions. If the blade is bent, warped or chipped, replace it.

For more mower troubleshooting advice and repair instructions, see our lawn mower repair help section.

Tools you need

• Torque wrench

• File

• Wood block

• Work gloves

Warning: Maintaining power tools can be hazardous. Use the proper tools and safety equipment noted in this guide and follow all instructions. Do not proceed until you are confident that you understand all of the steps and are capable of completing the maintenance. Some maintenance should only be performed by a qualified technician.

Step-by-step instructions

1. If you have a gas-powered mower, disconnect the spark plug wire. Carefully tilt the lawn mower on its side with the fuel tank fill hole facing up.

2. Put on work gloves to protect your hands from cuts. To immobilize the blade, wedge a wood block between the blade and a solid area of the mower housing. You can also use a blade-removal tool to remove the blade.

3. Remove the bolt and washer, and inspect the bolt. If the blade bolt is damaged, replace it with a manufacturer-approved bolt, rather than a standard bolt. Blade bolts often are specially designed and heat-treated to prevent failure that could cause injury or damage.

4. Secure the blade in a vise and sharpen the blade with a file. Follow the existing angle of the cutting edge and file in only one direction.

5. After sharpening, check that the blade is balanced. Drive a finish nail or casing nail into a wall and hang the blade horizontally, through the center hole. If one end dips, grind more from that end.

6. Use a torque wrench to reattach the blade, tightening the bolt to the torque specified in your owner’s manual—most blade bolts require around 45 to 55 foot-pounds of torque.

7. Set the mower upright and reinstall the spark plug.