Knowing the lawn mower spark plug size is essential when you need to replace damaged ones. However, some spark plugs can vary in size due to their manufacturer’s specifications.

Right Spark Plug for Your Lawn Mower

Using the incorrect spark plugs can have dire consequences for your mower. In this article, we will learn all there is to know about the spark plug size of your lawn mower.

How Do You Determine Your Lawn Mower Spark Plug Size?

💥 You can determine your lawn mower spark plug size by looking at the thread size, thread length, heat rating, and the spark plug gap. When it comes to the parts of all lawn mowers, picking the right size for the right piece matters greatly.


This is why the spark plug for a lawn mower is vastly different from that of an automobile.

– Check the Thread Size

The thread size is an essential determining factor when it comes to plug type and size. Selecting one that does not fit together will just not work when replacing a new mower spark plug in its socket.

Lawn Mower Spark Plug Guide

For this purpose, thread size is defined based on two categories, which are thread diameter and thread pitch. Thread diameter measures the width of your spark plug’s threaded section, whereas thread pitch indicates the distance between individual threads.

Forcing the wrong spark plug type will only damage your mower’s spark plug socket. This will result in a faulty engine, which could cause malfunction or worse, severe damage. Try to remember that most mower spark plugs have thread diameters that range between 10 millimeters and 14 millimeters while thread pitch is usually at 1 millimeter to 1.5 millimeters.

– Check the Thread Length

Another consideration we should factor in is the thread length of the spark plug. A mower spark plug has a thread length that is 3/8 of an inch long. The length is important because it will determine how deeply the plug will fit in the engine.

When spark plugs aren’t seated deep enough in their sockets, fuel or oil can accumulate around the tips. On the other hand, if spark plugs are screwed in too deep, then the buildup of gas or oil could cause overheating on the threads.

If the wrong thread length is used in the spark plug socket, then the cylinder of your lawnmower won’t be sealed due to the ill-fitting components. This will result in your engine having trouble starting, malfunctioning, or getting damaged.

– Determine the Type of Lawn Mower

Push mower spark plugs differ slightly from the ones used in riding mowers. To avoid using the wrong spark plug, here’s what you need to remember. You can read in more detail the differences between Push and Self propelled mowers.

Push mower spark plugs usually have pitch thread sizes of 1 millimeter to 1.5 millimeters. Aside from this, the thread’s diameter ranges from 10 millimeters to 12 millimeters. Their thread length or reach is from 9 millimeters to 12 millimeters.

Riding mower plugs have very similar dimensions to the ones used in push mowers. They also have a pitch of 1 millimeter to 1.5 millimeters, but this time, the diameter is slightly larger at 12 millimeters to 14 millimeters. The thread length or reach is also bigger at 15 millimeters to 19 millimeters.

What happens if you use the wrong type of spark plug for your mower? Lawn mowers require specific types of plugs to function correctly. If you use the incorrect type of spark plug, then your lawn mower could end up with some performance issues. Some indications include:

  • Misfiring engine
  • Rough time starting the engine
  • Fuel or oil accumulation on the spark plug
  • Overheating spark plug

– Check the Spark Plug Heat Rating

A spark plug also has a heat rating, which is the ability to tolerate specific levels of heat. The heat rating of the plug is measured in a standardized rating, which ranges from a scale of two to twelve.

Importance of Proper Spark Plug Size

The lower the number of the rating, the easier it will take for the plug to heat up. For instance, a spark plug that has a heat rating of six will easily overheat at a lower temperature compared to one with a heat rating of seven and up.

Using the incorrect heat rating may either cause your engine to experience pre-ignition or result in your engine having problems operating at any speed. Always use the plug with the appropriate heat rating for your lawn mower.

– Double-Check the Plug Gap

While you’re at it, consider inspecting the spark plug gap to determine if it is set at the correct distance. A plug has two electrodes that generate the spark that causes the engine’s ignition and combustion.

If the gap is too far apart, the plug will have problems igniting. If the gap is too close, there may not be enough air to cause combustion. Either way, the incorrect gap distance can be an issue later on. To resolve the gap, use a feeler gauge. This will allow you to determine if the gap adheres to the required size for the particular spark plug for your lawn mower.

– Other Tips and Tricks

Based on all the technical information you now possess, you are in a better position to determine the right size spark plug. A bad spark plug can be disappointing, especially when it is damaged. However, a bad spark plug doesn’t mean you can’t replace it.

Truth About Maximizing Lawn Mower Performance and Grass Damage

All you need to do is simply get a new one.

Here are some tips for you when replacing your old spark plug with a new one:

  • Always refer first to the owner’s manual of your lawnmower. Here, you will find the exact make and model, as recommended by the manufacturer, that you can purchase to replace your spark plug.
  • If you have misplaced or lost your copy of the owner’s manual, look up the owner’s manual online from the manufacturer. It will usually provide similar information as the physical copy.
  • Should the online owner’s manual lack the information you’re looking for, you can always send a message to the manufacturer’s email addresses or contact them at their phone numbers or social media.
  • Bring the spark plug with you when you purchase a new one. Attendants at the hardware store will be able to identify the spark plug type based on the sample you brought.

For those who are wondering if you can use your car’s spark plug for your lawn mower, the answer is a resounding no. While they may sound the same, they are made differently.

The spark plugs cannot be interchanged, and doing so will only result in engine damage. The same cannot be said with the oil, since you can use your car’s oil in a lawn mower.

– Be Aware of the Basic Components of a Spark Plug

A spark plug has several elements and features that not everyone knows. In order for us to fully understand this essential piece, we have to familiarize ourselves with its parts.

There are four basic parts of the plug, which are:

  • A threaded metal shell or casing
  • A live or central electrode
  • An insulator
  • A ground or outer electrode

Aside from these major parts, the plugs contain smaller pieces, such as a gasket, ring, and center shaft, among others. Based on the specified features, selecting the particular plug size should be easier.


The spark plug in your lawnmower is essential to powering it up, so finding the right size for it is incredibly important.

Let’s recap what we know:

  • Using the incorrect spark plug can result in engine performance issues or engine damage.
  • Always refer to the recommended spark plug size and type on your owner’s manual.
  • When in doubt, bring the spark plug with you as a reference when buying replacements.

You can now rest easy as you know more about your lawnmower’s engine spark plugs. Just remember our tips the next time you buy spark plug replacements!

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