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What Size Auger Do I Need For Fence Posts? Post Hole Digging With A Tractor: A Comprehensive Guide

What Size Auger Do I Need For Fence Posts? Post Hole Digging With A Tractor: A Comprehensive Guide

Written by: Mike Reese



Time to read 5 min

When it comes to post hole digging with a tractor, choosing the right auger size is crucial for getting the job done efficiently and effectively. The size of the auger needed will depend on various factors, including the size of the posts, the type of soil, and the depth of the holes required.

Generally, for digging post holes with augers mounted on tractors, you'll want bits that come in sizes ranging from 6 inches to 12 inches in diameter. While a smaller diameter auger may be suitable for smaller posts and softer soils, a larger diameter auger may be necessary for larger posts and harder soils. Additionally, the depth of the holes required will also play a role in determining the appropriate auger size.

Choosing the right auger size for post hole digging with a tractor can save time and effort in the long run, as it ensures that the holes are the right size and depth for the posts being used. With the right auger size, the job can be completed quickly and efficiently, allowing for a sturdy and secure fence or structure to be built.

Determining the Appropriate Auger Bit Size

When it comes to post hole digging with a tractor, determining the appropriate auger bit size is crucial for efficient and effective work. There are several factors to consider when choosing the right bit size for the job at hand. 

Factors to Consider

One of the most important factors to consider is the size of the posts that will be used. The auger size should be slightly larger than the diameter of the posts to allow for easy insertion and proper alignment. Another factor to consider is the type of soil that will be dug into. Hard, compact soils require larger auger sizes to penetrate and remove soil more effectively.

The tractor's horsepower and hydraulic flow rate are also important factors to consider. The auger size should be compatible with the tractor's capabilities to ensure efficient and safe operation. The maximum lift capacity of the tractor should also be considered to ensure that the auger can be lifted and moved easily.

Auger Bit Size Chart

Here is a general auger size chart for post hole digging with a tractor:


Post Diameter (inches)

Auger Size (inches)











It is important to note that this chart is a general guideline and may vary depending on the factors mentioned above. It is recommended to consult the tractor and auger manufacturer's specifications and guidelines for the most accurate information.

Our Recommended Sizes and Bits for Common Tasks

Setting 4x4 Fence Posts - 8" or 10" Earth Auger Bit

A common mistake when drilling post holes is to get the exact diameter bit that your post holes will be.

A 4x4 post, which has a 5" maximum width (diagonally), is definitely going to fit into a 6" hole -- but you're going to find out that you have almost no room to backfill with dirt or concrete to secure it.

That's not even considering having zero wiggle room if you need to align your post to be inline and level.

We recommend an 8" bit minimum for this job -- and we've got a fantastically engineered bit by Digga in both 8" and 10" if this is what you need.

Setting 6x6 Wood Posts - 12"+ Earth/Rock Combo Auger Bit

Similar to the 4x4 Post Setting recommendation -- A common mistake when drilling post holes for 6x6 Wood Posts is to get the exact diameter bit that your post holes will be.

We recommend a 12" bit for this job to ensure you have enough space to backfill with dirt, gravel, or concrete -- and considering the depth you'll likely need for a post this size, we recommend upgrading to a Rock / Earth Combo bit.

Again, we've really got to shout out Digga here for putting together a great combination bit -- an incredibly powerful pilot head to break up rock, and precision-engineered teeth to remove earth and rock shards up through your auger bit and out of the way.

Benefits of Using the Right Auger Size

One of the main benefits of using the right auger size is that it saves time and effort. A properly sized auger will make the job quicker and easier, allowing the operator to move on to other tasks. Additionally, using the right size auger will result in a cleaner and more precise hole, which is important when it comes to setting posts for fences, decks, or other structures.

Another benefit of using the right auger size is that it reduces the risk of damage to the tractor or other equipment. Using an auger that is too small or too large can put unnecessary strain on the tractor's hydraulic system or cause the auger to become stuck in the ground, resulting in damage to the equipment.

Consequences of Using the Wrong Auger Size

Using the wrong size auger can have several negative consequences. One of the most common issues is that it can result in a poorly dug hole. If the auger is too small, the hole will be too narrow and may not provide adequate support for the post. If the auger is too large, the hole may be too wide and require more concrete or other materials to fill, resulting in unnecessary expense and wasted resources.

Another consequence of using the wrong size auger is that it can increase the risk of injury. If the auger is too large, it may be difficult to control and could cause the tractor to tip over. If the auger is too small, it may not be powerful enough to dig through hard or rocky soil, causing the operator to apply excessive force and potentially injuring themselves.

Overall, using the right size auger is essential for efficient, safe, and effective post hole digging with a tractor. By taking the time to select the appropriate size auger for the job, operators can ensure that they get the job done right the first time, without wasting time, effort, or resources.

Maintenance and Safety

Maintaining Your Auger

Regular maintenance of your auger is essential to ensure it is working properly and safely. Here are some tips:

  • Inspect and maintain equipment properly.
  • Make sure the cutting blade is sharp.
  • Ensure all shields are tightly attached.
  • Check for fluid leaks.
  • Inspect hydraulic hoses for cracks and weathering.
  • Use shear bolts provided by the manufacturer only.
  • Grease frequently and check wear spots and shear bolts.

By keeping your auger in good condition, you can prevent damage to the equipment and avoid potential accidents.

Safety Precautions

Augers can be dangerous if not used properly. Here are some safety precautions to keep in mind:

  • Keep everyone but the tractor driver at a safe distance when an Auger is in use.
  • Never allow anyone to stand in the auger's path or near the tractor while it is in operation.
  • Wear appropriate clothing, including eye protection and sturdy shoes.
  • Be aware of your surroundings and any potential hazards, such as underground utilities.
  • Never attempt to clear a jammed auger with your hands or any other body part.
  • Always follow the manufacturer's instructions for safe operation.

By taking these precautions, you can avoid accidents and ensure that your post hole digging project goes smoothly and safely.


Overall, the main thing to take away from this article is that you always want to drill a hole bigger than your fence post and fill it in afterwards rather than drill a hole that is too small.

Complications with ground type and soil makeup, as well as the difficulty of digging out a vertical hole are all reasons why we strongly suggest digging holes that are larger than your fence post in line with the recommendations of our table above.