Pergola Post Size 4×4 or 6×6: Which One is Best for Your Project?

Want to find the best pergola post size?

4×4 posts will suffice for a pergola with a post distance of 4 to 6 feet and a height of less than 3 feet.

However, most experienced contractors recommend using 6×6 for the pergola post size.

We’ll help you decide which is best- 4×4 or 6×6 for your pergola.

The 4×4 posts cannot carry as heavy a load and may warp or bend over time, causing a safety concern.

If you want the post to resist twisting, the 6×6 pergola post size is your better choice.

Many homeowners dream of a beautiful pergola as an extension of their outdoor living space.

However, building a sturdy pergola can be a challenge for those attempting a DIY project without proper research on the correct pergola post size.

The first decision to make when choosing your new pergola correctly is a simple one: 4×4 or 6×6 pergola post size. Does it make a difference?

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There are excellent reasons to choose 6×6 posts over 4×4 posts, more than safety concerns.

Please read on for more information to help you with your project.

Man holding a 4x4 post for pergola post size

Related Reading: Difference Between Pergolas, Ramadas, And Gazebos

Load Bearing Pergola Post Size

So, one of the main things to consider before building a pergola is how much weight it is expected to support.

You don’t want your relaxing evening out on the porch interrupted by your pergola coming down, so it’s worth doing some calculations before you start building.

Finding the right pergola post size is one of the most critical decisions.

How much weight a post can bear is impacted by several factors, such as:

  • Species of Wood
  • Wood Grade
  • Load Type
  • Whether or not it’s Pressure-Treated
  • How high off the ground

Vertically, at 3 feet, a #2 grade 4×4 post can support approximately 17,000 pounds depending on the wood grade, load type, and species.

The 6×6 post will handle about 20,000 pounds.

But if you want a taller pergola post size, the load-bearing decreases significantly.

Selecting the taller 8-foot 4×4 post will support approximately 6,500 pounds, decreasing even further to 2,300 pounds at 14 feet high.

The 6×6 post at 8 feet tall will support approximately 18,000 pounds, with a 14-foot high bar that will handle 10,500.

Please keep in mind the reduction in weight support as the post size increases in length.

The conclusion is that naturally, you should do the lumber calculations for your pergola to ensure you have the right pergola post size.

As a general rule, a 6×6 bar will not make much of a difference for posts shorter than 3 feet, but above 3 feet, use one.

While a 4×4 post can last up to 40 years with proper treatment, a 6×6 post is more durable due to its larger size.

Related Article: Douglas Fir or Cedar for a Pergola: Choosing the Best Wood


Another factor that makes a 6×6 post a better pergola post size than a 4×4 is the possibility of notching them.

Notching involves cutting a groove into posts to fit other pieces of wood.

This may be done for aesthetic reasons or by being able to add items such as rim joists.

But be aware that it creates a weak point in the post.

Naturally, the thicker post will survive this weak point better than a thinner one, meaning that a 6×6 post will do you better if you plan to add any notching.

Notching can be helpful in offering an entire beam stability to support a header or other heavy items.


Weather is another reason to choose 6×6 posts over 4×4 as the better pergola post size.

But, if you live in an area with an excess of snow and ice that puts a lot of pressure on your deck – literally!

If snow builds up, a 4×4 post might not be able to withstand the weight, which could have disastrous consequences for your pergola.

6×6 posts are more stable in colder climates and can carry heavier loads, securing your roof better.

I have another article that may be helpful regarding a solid roof on a pergola. Link below.

Related Article: Solid Roof on a Pergola: Exploring Your Options


The expense is one of the most significant and impactful factors that may make someone choose one kind over the other.

In some surface-level research, 4×4 posts can be around $40, while 6×6 posts start at $94.

However, as many experienced contractors would recommend, the benefit offered by using a 6×6 post would far outweigh the price difference.

Please remember the following guidelines: If the pergola is taller than 3 feet, 4×4 posts run the risk of bending over time or, even worse, collapsing under the weight of general use.

In any other case, where the pergola is 3 feet or under and has 4 -6 feet space between posts, 6×6 posts are recommended for superior support.



A small but important note to end this article on the best pergola post size.

One factor that could give an advantage to 6×6 over 4×4 is the specific codes or laws that regulate your area.

Depending on where you live, it may be nothing short of a legislative requirement to use 6×6 posts in your project.

It depends highly on where you are, so check your local laws.

Related Article: Determining the Ideal Pergola Beam Size: Expert Advice


For many reasons, 6×6 posts are a clear choice, with few benefits to 4×4 posts.

Advantages involve the fact that:

  1. 6×6 posts can carry loads up to 78% more than 4×4 posts at 14 feet.
  2. 6×6 posts are much easier to apply to notch.
  3. 6×6 posts are more durable against weather conditions. More ability to hold snow and withstand high winds.
  4. 6×6 may be required by legislation, depending on where you live.

Their only true advantage of 4×4 posts over 6×6 posts is the price.

Price should not be a deciding factor when finding the optimum pergola post size.

However, there are few exceptions to using 4×4 posts, as 6×6 posts are usually more stable.

The only exceptions to 6×6 posts instead of 4×4 are posts below 3 feet and pergolas with 4 to 6 feet between bases.

We want a beautiful pergola that’s within budget but never compromising safety.

Enjoy living the outdoor life!