4x4 or 6x6 for Retaining Wall

4×4 or 6×6 for Retaining Wall-[Explained!!]


While building a retaining wall, it’s easy to get confused about the right measurements. We know how much of a hassle it could be. 

So, you are wondering about 4×4 or 6×6 for retaining wall?

The 6×6 retaining wall has a higher retaining capacity. Its added height, base, and thickness can retain more soil than the 4×4. Although, for a typical garden, a 4×4 retaining wall is enough. Also, it costs quite lesser in your pocket. Because of the added materials, the 6×6 costs more. 

But knowing only this much isn’t enough. Don’t worry though cause we’ve written a whole article explaining the factors. 

4×4 or 6×6 for Retaining Wall- Quick Comparison

While the construction process lies the same for both, there are certain criteria to consider. We know how important it is for you to be aware of all the facts. That is before getting into action. 

So, we’ve done the groundwork for you. Hopefully, this brief table will give you a concept about which things to take into consideration: 

Ground of Comparision



Retaining Capacity

15500 - 16500 lb(7000 - 7500kg)

23500 - 24500 lb(10000 - 11000 kg)


Depth: 5-6 inch

Depth: 7-inch


Base thickness: 12-inchStem thickness: 7 inch

Base thickness: 12-nchStem thickness: 7.5 inch


Stem building material: Cheap build: 32$-36$Expensive build:160$-240$

Stem building material:Cheap build: 72$-108$Expensive build: 360$-540$

Surely enough though, these brief pieces of information won’t be able to satisfy your curiosity. That’s why we’ve tried to elaborate on them further. 

4×4 or 6×6 for Retaining Wall- Detailed Comparison

We know how every little detail counts while making a decision. Also, information may vary on your particular circumstance. 

So here we have tried to explain all the factors in as much detail as possible. Be sure to go through all of it. 

Retaining Capacity

For a retainer wall, the first thing that comes to mind is soil amount. That is the amount of soil it can retain. The pressure created by the soil has to be retained by the wall. 

Surely, the 4×4 and 6×6 walls have different traits in this case. 

Even if we don’t consider the foundation, the stem is enough to describe it. The 6×6 retainer wall is bigger than the 4×4 wall. That is in both height and width. 

So it is able to cover more area and block more soil. 

Also, the materials used in the 6×6 retainer wall outweigh the 4×4. This results in more pressure counter than the 4×4. The added soil pressure can be bared by the 6×6 retainer wall. 

You might think of lowering the height and width but keeping the same amount of soil. This won’t work. If you try to retain soil more than the 4×4’s ability, it will simply break. That is due to the pressure over time. 

So, how much soil can a 4×4 retainer wall retain? For a 4×4 wall, you can expect it to retain 7000-7500 kg or 15500-16500 lb of soil. 

And, how much soil can a 6×6 retainer wall retain? For a 6×6 wall, you can expect it to retain 10000-11000 kg or 23500-24500 lb of soil. 

Although, these are just approximate values. These numbers may differ on the type of wall you are using too. 

A concrete retainer wall will be able to retain more soil than a timber-built retainer wall. It will last for longer too. 

Not only that but the type of soil you want to retain may also change the values. As different types of soils apply different amounts of pressure on the wall. So, the values might differ. 

Also, there has to be a certain distance between the house and the retainer wall. Your house might also need work and you wouldn’t want it to affect your retainer wall. 

For a house, you should know how much time it takes to do house after drywall

But you can trust the numbers that are provided as they are calculated considering your circumstances. 

So, judging from all this, what should you do? If you are an average homeowner with a garden, go for the 4×4. It would be more than enough for you. 

On the other hand, you might have a big garden and plans. In that case, the 6×6 is the perfect choice for you. 


The base or foundation of a retainer wall is a really essential part. 

A strong base is the main source of strength for your retainer. If it isn’t strong enough then the wall won’t be able to support the soil. It will break or fall apart from the pressure of the soil. 

If a base is bigger and deeper, it can support a larger stem wall. That means you’ll need a deeper base for the 6×6 retainer wall. The added weight of its stem wall requires this additional depth. 

So, how deep should my 4×4 retainer wall base be? The base for your 4×4 retainer wall should be between 5-6 inches. 

And, how deep should my 6×6 retainer wall base be? The base for your 6×6 retainer wall should be about 7 inches. 

So, what’s the general principle in building a retainer wall base? Among its whole depth, you should fill about 3 inches with gravel. Then the rest of the depth is to cover half of the first row of blocks. 

Although, this is not true for walls that are not made for home purposes. For much larger retaining walls, it can be a complicated process. As it has to withstand much more pressure, it is built more strongly. 

For that, first, a foundation-like structure is made on a concrete layer using rebars. Two sets of rebars are set on each other. Upon that the rebars of the stem wall stand. 

Then, another set of rebars is used to lock them in the foundation. Later, the whole hole is cast with concrete. Thus the structure becomes quite a formidable one. 


For the thickness too, the 4×4 and 6×6 are different. Since the 6×6 wall has a bigger stem wall, it is natural to be thicker. 

If you only increase the retainer wall in length and width, it won’t be able to hold. For a fixed amount of volume, there will be more pressure than the wall can withstand. 

So, increasing the thickness is a must. 

Now, how to calculate retainer wall thickness? There are two simple formulas you can follow to calculate this:

           Base thickness= ⅛ to the stem wall height (can’t be less than 12 inches)

           Stem thickness= 6 inches + ¼ inch per foot (stem wall height)

Now, let’s calculate the thickness of our retainer walls. So, what should be the thickness of the 4×4 retainer wall?  In this case, our stem wall height is 4 feet or 48 inches. Thus,

The Base thickness of 4×4= ⅛ x 48= 6 inches

But, the base thickness can’t be below 12 inches. So the base thickness for our 4×4 would be 12 inches. 

Stem thickness of 4×4= 6 +( ¼ x 4)= 7 inches

So, the stem thickness for the 4×4 retainer wall will be 7 inches. 

Now, what should be the thickness of the 6×6 retainer wall? For this, our stem wall height is 6 feet or 72 inches. Thus, 

The Base thickness of 6×6= ⅛ x 72= 9 inches

Again, the base thickness can’t be below 12 inches. So, the base thickness for our 6×6 will be 12 inches too.

The stem wall thickness of 6×6=6+ (¼ x 6)= 7.5 inches

As we can see, in terms of thickness the 6×6 outdone the 4×4 retainer wall. So, if you need the added thickness to support your soil, choose 6×6. 


The last thing to consider is price. Since the 6×6 uses more material, obviously it’ll cost you more. Here, let’s try to establish a value: 

Rather than the whole project cost, let’s focus on different sectors. The first thing you have to consider is the material price. 

The cheapest material could be cinder blocks. They’ll cost you about 2$-3$ per square foot. On the other hand, you can go for metal along with caulk which are much more expensive. They’ll cost you 10$-15$ per square foot. 

Here are some suggestions for you:

So, for the 4×4 retaining wall, the area of the stem wall is 16 square feet. Thus the cheapest build would cost= 16 x (2$-3$)= 32$-36$

On the other hand, the expensive build will cost= 16 x (10$-15$)= 160$-240$

And, for the 6×6 retaining wall, the area of the stem wall is 36 square feet. Thus the cheapest build would cost= 36 x (2$-3$)= 72$-108$

Also,  the expensive build will cost= 36 x (10$-15$)= 360$-540$

Thus, we can see that the costs are much more for the 6×6. Also, you mightn’t want to do the work yourself. then you’ll have to consider the labor charges too. It will cost you about 10$-30$ per square foot.

Also, the decoration matters. Maybe you’re sitting on your deck and the sight of your beautiful retaining wall charms you. An interesting fact about decks is, before or after deck siding. 

So, if you are running low on your budget, then it’d be wise to choose 4×4. 

What to Choose?

By now you should be able to guess which one is right for you. If you want more retaining capacity then go for the 6×6. Its deeper base and the thicker wall will be able to retain more soil.

Although, if you are concerned about the money, then go for the 4×4 retainer wall. It’ll cost you much less than the 6×6 retainer wall. 


What is the best retaining wall height?

In the best-case scenario, a retaining wall should be roughly five feet tall. Sandy soil with good drainage is the ideal type of environment for constructing a retaining wall. Clay-rich soil puts considerable strain on the new wall. Also, the wall is made even heavier by moisture.

What is the best option for retaining walls?

The strongest and longest-lasting option for retaining walls is poured concrete. Depending on your preference, it can also be carved and shaped to resemble mortared stone. Although, garden retaining walls do not need such a strong structure. It is used for other more complicated reasons.

Why does the retaining wall fail?

Poor drainage is the primary reason for retaining wall failure. Hydrostatic pressure accumulates behind the retaining wall in the absence of appropriate drainage. Saturated earth is much heavier compared to dry soil. Thus, the retaining wall might not be able to support such a load.

Bottom Line!!

Now let’s hear from you. 

Were we able to solve all your queries related to 4×4 or 6×6 for retaining wall?

Here’s some extra information for you. Be sure to ensure proper drainage for your retainer wall. 

If there’s anything else left on your mind, be sure to comment down below.

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