how many bags of concrete you need for a fence post

When you're installing a fence post, the amount of concrete you need will be calculated based on the diameter of your fence post and how high the post is above ground.

Most fence post holes will need between 1 - 4 bags of concrete to securely hold the post in place.

The best way to determine the size of the hole is:

  • Diameter of the hole is 3 times the width of the fence post
  • Depth of the hole is one-third to half the above ground height of the fence post

For example: A 6' high fence post 4"x4" needs a hole 12" in diameter by about 2' to 3' deep. That would take four 50 lb. bags of fast setting concrete mix per fence post.


How much concrete for a fence post

how much concrete for a 3" diameter fence post?

A fence post 3" in diameter will need a post hole that's 9" in diameter and a depth of at least 1/3 the height the post is above ground. A 6' high post will need a 2' deep hole.

For a 9" diameter hole, the table below will show you how many bags of concrete you need based on the depth of your hole.

Depth of hole in inches

10 - 12 inches

14 - 26 inches

27 - 36 inches

# of 50 lb. bags of concrete needed

1

2

3

These figures are based on a fence post that's 6' above ground and 2' below ground.

how much concrete for a 4" diameter fence post?

A 4" diameter fence post will need a post hole that's 12" in diameter and a depth of at least 1/3 the above ground height of the fence post.

The table below shows you how many bags of concrete you need per post for a 12" diameter hole that's between 12" and 36" deep.

Depth of hole in inches

10 - 14 inches

16 - 22 inches

24 - 30 inches

32 - 36 inches

# of 50 lb. bags of concrete needed

2

3

4

5

These figures are based on a fence post that's 6' above ground and 2' below ground.

how much concrete for a 6" diameter fence post?

A 6" diameter fence post should have a post hole that's 18" in diameter and a depth that's at least 1/3 the above ground height of the post.

The table below shows you how many bags of concrete you'll need per fence post for a 18" diameter hole that's between 10 - 36 inches deep.

Depth of hole in inches

10 - 12 inches

13 - 17 inches

18 - 21 inches

22 - 25 inches

26 - 28 inches

28 - 30 inches

32 - 36 inches

# of bags of 50 lb. concrete needed

4

5

6

7

8

9

11

These figures are based on a fence post that's 6' above ground and 2' below ground.

post hole concrete calculator

This concrete calculator will help you figure out how many bags of concrete you need per post hole.

Enter the diameter of your post, then the diameter and depth of your post hole.

Next, enter how many post holes you have to fill and click on "Calculate".

The concrete calculator will tell you how many cubic yards of concrete it'll take. (just in case you have a lot of holes to do.)

Using ready-mix concrete might be a better solution than using bagged concrete if you have a lot of them to do.

The calculator also tells you how many 50 lb., 60 lb., and 80 lb. bags of concrete you need.

This gives you the option to use a larger size bagged concrete mix than what is in the charts above and know how many to get.

You can order 1 cubic yard of ready-mix concrete but understand, the concrete company will charge you for a small load charge that could be several hundred dollars.

Most concrete companies charge some kind of small load charge for any orders under 5 cubic yards. 

Call your local ready-mix plant to find out what they charge in your area.

How Many Bags of Concrete Needed For a Post Hole

7 steps for setting a fence post in concrete

STEP 1. Using a post hole digger, dig your post hole so the diameter is three times the width of your fence post.

Example: For a 4" wide post you'll need to dig a hole that's 12" in diameter.

The depth of the hole should be at least 1/3 the above ground height of the post.

Example: For a post 6' above ground, you should dig a hole that's 2' deep.

How many bags of concrete you need for a fence post

If you have a lot of holes to dig, this gas powered posthole digger will be a lot faster.

STEP 2. Add about 6" of gravel into the bottom of the hole.

Compact the gravel by tamping it with your post or by using a 2 x 4.

If you don't have your own gravel then use something like Quikrete crushed gravel.

bags of concrete per fence post

STEP 3. 

Set the fence post in the center of the hole and attach some 2 x 4 braces to hold it plumb.

You can also use this post bracing kit to hold the fence post in place while the concrete sets up.

The post kit is available to purchase on Amazon.

how much concrete for a fence post

STEP 4. 

Use a level to plumb the post vertical. 

Once the post is in place, use your 2 x 4's or the post kit to secure the post in place.

You don't want the post to be out of plumb when the concrete starts to set up.

How many bags of concrete for a fence post?

STEP 5. 

Fill the hole with some fast setting concrete mix.

Use enough dry concrete to fill the hole up to about 3 - 4" below ground level.

post hole concrete calculator

STEP 6. 

Wet the concrete by adding about a gallon of water per 50 lb. bag of concrete mix.

Let the water slowly soak into the concrete and completely saturate it.

The fast setting mix will set hard in about 20 - 40 minutes.

number of concrete bags needed for a fence post

STEP 7.

Allow the concrete to set up for at least 4 hours before you start to build your fence.

If you used a fast setting concrete mix, it will be strong enough to support weight at this time. 

If you used regular concrete mix, wait until the next day to start building your fence.

concrete bags for a fence post

what is the best concrete mix for fence posts?

The two best concrete mixes for setting fence posts, in my opinion, are:

Both these concrete mixes are a "just add water" type of concrete. That means you don't have to pre-mix the concrete before you put it in the hole. 

They both set up in 20 to 40 minutes which helps speed up your fence installation.

If you're not in a hurry, then any regular concrete mix will work just fine. If you use a regular setting mix instead of a fast set mix, you'll just have to wait until the next day to start building the fence.

should fence posts be set in concrete?

Your fence is only going to be as strong as the posts that are supporting it. In most cases, it's much better to embed your fence posts in concrete.

Whether you have wooden or metal fence posts, setting them in concrete ensures you'll have a strong stable base for your posts.

Here's a few things to consider when setting your posts in concrete:

  1. When choosing a wooden fence post, pressure treated posts will give you the best long-term performance. Cedar and Redwood posts are also very good as they both have a natural resistance to rotting and decay.
  2. If you use a wooden post made of spruce, oak, or pine, make sure you treat the wood with a preservative like Rust-Oleum Woodlife below-ground wood preservative or the post will rot and break.
  3. Make sure to use a base layer of pea gravel or crushed stone under the concrete so rain water can drain into the surrounding soil and not puddle around the fence post.
  4. Taper the top of the concrete away from the embedded fence post to help drain rain water away from the post. The less water that gets in between the concrete and the post the better.
  5. Caulk the seam around the post where it comes out of the concrete. If you notice a small seam where the wood shrunk away from the concrete, use some acrylic latex caulk to fill the seam and prevent water from getting in there.

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