Fence Post Concrete Calculator
Calculate exactly how many bags of concrete you need for fence posts, deck footings, and piers. Estimates volume for round or square posts in post holes.
1. Hole Details
2. Post Details
Use 3.5 for a 4x4 post, 5.5 for a 6x6.
About the Concrete Calculator for Post Holes
Setting fence posts, deck footings, or pergolas requires precise planning. This concrete calculator for post holes determines the exact amount of pre-mix concrete required to fill the void between your post and the earth. By calculating the net volume (Hole Volume minus Post Volume), you avoid buying too many bags or running out mid-project.
How to use the Fence Post Concrete Calculator
- Hole Dimensions: Enter the diameter of your auger or digger and the depth of the hole.
- Post Size: Specify if you are using a square post (e.g., 4x4, 6x6) or a round post.
- Quantity: Enter the total number of posts for your fence line.
The calculator instantly displays the number of bags needed. For large commercial jobs, it also provides the cubic yardage for ordering a truck.
Fence Posts Concrete Calculator Tips
- 4x4 Posts: Actual dimensions are typically 3.5" x 3.5".
- 6x6 Posts: Actual dimensions are typically 5.5" x 5.5".
- Frost Line: Always dig below the frost line in your area to prevent heaving.
- Gravel Base: It is common practice to put 6 inches of gravel at the bottom of the hole for drainage. Do not include this gravel depth in the concrete calculation.
Concrete Pier Calculator for Sonotubes
This tool also functions as a concrete pier calculator. If you are pouring concrete piers (sonotubes) without a post inside, simply select "No Post" in the options. This will calculate the full volume of the cylinder.
For flatwork projects like patios, use our General Concrete Calculator or the Concrete Bag Calculator for slabs.
Post Hole Concrete Estimations
A standard 4x4 fence post in a 10-inch diameter hole, 24 inches deep, typically requires about 1.5 bags of 60lb concrete. However, this varies significantly based on how consistent your hole width is. We recommend over-ordering by 10% to account for irregular hole shapes.
? Frequently Asked Questions
For a standard 4x4 post in a 10-inch wide hole (2 feet deep), you typically need about two 50lb bags or one-and-a-half 80lb bags.
Most experts recommend placing 6 inches of gravel at the bottom for drainage, then setting the post, then pouring concrete around it.
Yes, select 'Round' in the Post Shape options and enter the diameter of the post.
A general rule of thumb is the hole diameter should be 3 times the width of the post. For a 4-inch post, a 12-inch hole is ideal.