How to measure a mower blade

Why it matters: What blade does my lawn mower use?

Grabbing a "close enough" blade off the shelf might seem fine, but the wrong size can lead to poor cutting performance—or even damage your mower. A mismatched blade could hit the deck, rattle loose, or just make your lawn look uneven.

If you've lost the manual (or never had one), the blade size won’t be listed on the mower itself—but you can still figure it out. The key measurements you'll need are:

• Blade length

• Center hole type and diameter

• Blade width (optional but helpful)

Once you've got those details, you can match them to the correct replacement blade for your mower.

How to measure a mower blade

Here's what to grab before you start:

Tape measure or ruler

A flat, stable surface

Work gloves (because blades are, well... sharp)

Your current mower blade (removed from the mower)

Tip: Make sure the blade is clean and straight—bends or warping can throw off your measurements.

Step 1: Remove the blade

Unplug your mower or disconnect the spark plug wire (safety first!). Flip the mower on its side and use a blade removal tool or wrench to remove the blade bolt. Wear gloves—it might be greasy or sharp.

Step 2: Measure the blade length

Lay the blade flat and measure diagonally from the tip of one cutting edge to the tip of the other. This is the full length.

Note: Blade length is typically a little smaller than the mower deck size. For example, a 22-inch mower may use a 21-inch blade. Riding mowers may use blades of different lengths depending on deck size and how many blades it uses—so always measure each blade individually.

Important: Don’t measure straight across the center—that’ll give you a shorter and incorrect length.

Step 3: Measure the center hole

Check the center of the blade. Is it a round hole, a star shape, or something else?

• Round hole – Measure the diameter in inches or millimeters

• 5-point or 6-point star – Count the points and match to your new blade

• H-pattern or bow tie – Unique to some manufacturers; shape must match exactly

Matching the hole type is critical—if it doesn’t match your mower spindle, the blade won’t fit (or worse, could fly loose).

Step 4: Measure blade width and thickness (optional)

Not always required, but helpful:

• Measure the width at the widest part

• Thickness is usually standard, but if your blade looks unusually slim or heavy-duty, take note

Types of mower blades

When shopping for a replacement, you’ll see different blade styles. They’re not all interchangeable—choose the one that matches your mower’s design and how you want to cut. For a deeper look, check out our video guides to types of riding mower blades and types of walk-behind mower blades.

Standard blades (lift blades)

• Common for side-discharge mowers

• Straight or slightly curved edges

• Great for regular mowing and bagging

Mulching blades

• Curved, with extra cutting edges

• Chop clippings into fine mulch

• Ideal if you leave grass clippings on your lawn

High-lift blades

• Steeper blade angle

• Create more suction for bagging

• Not great for sandy or dusty lawns

Using your model number (if you have it)

Without a doubt, using your model is the easiest way to find the correct blade. If you know your mower’s model number (usually found on a tag under the deck, near the engine, or under the seat), you can look up compatible blades directly. You can also search by part number if you're replacing the original OEM blade.

But if that model tag is worn out or missing, don’t worry—you can still measure the blade and find a match.

Need help finding the right fit? We’ve got a full collection of lawn mower blades that are easy to browse through.

Where to find your mower’s model number

Walk-behind mowers:

Check the top or side of the mower deck, near the rear wheels, or on the engine housing.

Riding mowers:

Look under the seat, near the rear wheels, or on the mower deck. Some models also place the tag near the engine or battery tray.

The model number usually includes a mix of letters and numbers and may appear next to the brand or serial number.

Extra tips: safety and when to replace your blade

Measuring your blade correctly is important, but so is staying safe while doing it—and knowing when it’s time to stop measuring and just replace the thing. Here are a few practical tips to help you handle the job safely and recognize when your blade has reached the end of the line.

Safety tips when measuring or replacing a blade

Before you dive into removing or inspecting your blade, make sure you're not setting yourself up for scraped knuckles or worse. A few quick safety steps can go a long way.

• Always disconnect the spark plug wire or unplug the mower before removing the blade

• Wear work gloves to avoid cuts

• Tighten the blade securely when reinstalling

• Replace any blade that’s bent, chipped, or cracked

Also, take a moment to check the rest of your mower—especially the deck and drive system. A new blade won’t help much if the rest of the mower’s in rough shape.

When to replace your blade

Wondering if it’s time for a new one? Here are some signs:

• Blade is visibly chipped or bent

• Grass looks ragged or torn after mowing

• Mower vibrates more than usual

• You’ve already sharpened the blade a few times

Most blades need replacing every 1–3 seasons, depending on how often you mow and what kind of terrain you’re dealing with.

Final thoughts

Knowing how to measure a blade doesn’t take long, and it can save you from the frustration of ordering the wrong part. Whether you’re replacing a mulching blade or just refreshing your regular mower setup, a few simple measurements can make a big difference in performance.

Ready to track down the right blade? We’ve got everything you need—from replacement blades and maintenance parts to step-by-step mower repair help—to help you get the job done and keep your lawn looking its best.