This Quikrete Calculator for Posts computes the volume and weight of Quikrete Concrete required to fill any given size hole with a 4×4 post.  To use this Quikrete Concrete Calculator for square posts just input hole diameter, hole depth and also the number of post holes. The output computes the total amount of Concrete needed and number of 40 pound, 60 pound, or 80 pound bags.  See below for more detailed information.  If you need more help on concrete requirements here is the 2012 International Code for Residential Buildings.4x4 Fence Post Concrete Calculator

Details about the Quikrete Concrete Calculator that computes the volume of the space between a 4×4 post and any diameter hole larger than 5-inches.

by Titus Nelson, PE

Inventor of the Holey-Moley Digger

The output is in (cubic inches) and (cubic feet).  In addition, the quick computation shows the amount of Quikrete in (pounds) to fill the void.  Quikrete weight is 133 lb/cuft for these calculations.  In addition, when you input the total number of fence posts, the total Quikrete requirement is output.  The total number of bags of Quikrete for your job is also shown for 30, 60, and 80 pound bags. As a result, the Quikrete Concrete Calculator uses these bag sizes.

Another point to remember is that filling the hole a few inches below the ground level will require less concrete. Because the Quikrete Concrete is below the ground, less moisture will accumulate which reduces moisture rotting of fence posts.  Therefore,  reduce the depth of your hole by the distance you want the concrete underground.

Actual 4×4 Square Post Dimensions

In conclusion, it is important to note that a nominal 4×4 post is actually 3.5″ x 3.5″ and the diagonal is 4.95″.   The minimum hole diameter required for a 4×4 post is therefore 5 inches. This makes for a tight fit requiring almost no concrete.

The Holey-Moley Digger Head Sizes are perfect for computing Quikrete requirements around 4×4 posts

The Holey-Moley Digger comes with standard digging heads of 4 inch, 5 inch and 6 inch.   As a result, the digger produces very straight and uniform holes. Therefore the Quikrete Concrete Calculator for the difference between the 4×4 post volume and the hole volume will be fairly accurate. Using these numbers will be quite accurate for 4×4 square posts.

In addition to calculators there are noteworthy blog article on this web page.  One describes Selecting The Best Hole Digging Shop Vacuum.   Likewise, another great article is Digging Deep, Straight, Uniform Holes with a Shop-Vac.  Please let us know how you like these calculators, we love feedback.  Finally, if you would like to be kept up-to-date on blog articles please sign up for more information here.

About the Quikrete Concrete Calculator for Posts

This Quikrete Concrete Calculator outputs the hole volume in cubic inches. Likewise, the space between the post and hole wall is provided in cubic inches.   In addition, you will also find these values in cubic feet.  Since concrete comes in bags by weight, output is also shown in pounds.

Input (inches)

1. Select or Input the Hole “Diameter” in inches.

2. Select or Input the Hole “Depth” in inches

3. Select or Input the number of posts

Output (Volume & Weight)

1. Hole Volume – Cubic Inches

2. 4 x 4 Square Post Volume Underground – Cubic Inches

3. Volume Around the Post – Cubic Inches

4. Volume Around the Post – Cubic Feet

5. Quikrete Required Per Post – Pounds

6. Quikrete Required For Job – Pounds

7. Number of 40 Pound Bags Required

8. Number of 60 Pound Bags Required

9. Number of 80 Pound Bags Required


In contrast to many calculators, this Square Post Concrete Calculator makes it easy to calculate the weight of concrete needed to fill a post hole of given diameter with a 4 x 4 post inside.  As a result the output conveniently provides the number of bags of various weights that you will need.

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