Wondering how many bags of concrete per fence post are needed, look no further here is the detailed solution. Using the right amount of concrete is very important so that your fence remains strong and sturdy at the same time you may not do the over-concreting which may increase your overall cost.
Generally, 1-4 bags of concrete per fence post is needed. It depends on various factors like the type of soil, fence design and height, size of post and size of the concrete bag, climate etc. ( i.e. the weight of the bag e.g. 40 lb or 50 lb).
Size of Post
The size of the hole should be 3 times the size of the post. For a 3-inch post, typically a 9-inch post hole is required to have a strong and stable fence. For a 4-inch post, a 12-inch hole is required.
Size of hole= 3 x Size of post
Fence height
To secure the fence post in its place, the depth of the post should be 1/2 to 1/3 of the post height. e.g. for a six-foot high fence, (6/2 = 3, 6/3 = 2), a 2 to 3 feet deep hole is required. A layer of gravel at least 6 inch depth is also required thus for a 6 feet high post you need to dig 2 feet + 6 inches to 3 feet + 6 inches.
Depth of hole = 1/3 to 1/2 of post height
Type of Soil
Soil with gravel and rock provides extra stability to the fence, however, they are difficult to dig. Sandy soil is easy to dig but it doesn’t stick to its place thus you will end up with a bigger diameter hole than that required. clayey soil is good however with moisture its volume changes, there is the problem of drainage with clayey soil. The soil type dictates the depth you need to go for your fence post.
Fence design
The heavy fence needs more depth than a lighter fence to have strong and stable posts. Thus if you are installing a heavy fence, then you should dig deeper to ensure the stability of your fence post.
Climatic Conditions
Areas prone to heavy winds require deeper fence posts than the areas where no heavy wind occurs. Similarly, for areas subjected to heavy rains/snow, the soil becomes loose and your fence post may tilt, for such areas you need more depth of fence post.
Frost depth
Frost depth is a depth at which the soil freezes permanently, you should know the depth of frost in your area as it will affect the stability of your fence post. Your post should go beyond the frost depth to have a stable fence post.
Method of Drilling
The method of drilling or digging also affects the number of bags of concrete. If you are digging the hole using Showel you may end up with a much bigger hole than required and more cement bags will be required. If you use an auger, you may dig the hole as required
Table of Contents
How many Bags of Concrete per Fence Post
To calculate how many bags of Concrete per fence post is needed you should first know the diameter and height of the fence post. From the diameter and height input, you can calculate the diameter of the hotel and the depth of the hole. The stepwise procedure is as under:
Step-1 Determine the diameter of the hole
The diameter of the hole should be 3 times the diameter of the fence post. For a 6-inch fence, (6×3=18) an 18-inch hole is required.
Step 2 Determine the depth of the hole
The depth of the hole should be (1/3 to 1/2) of the fence height (source). For a 6 feet-high fence, ( 6/3 to 6/2) i.e. 2 to 3 feet deep hole is required. don’t forget to add an extra 6 inches for gravel.
Step 3 Determine the volume of the hole
- The volume of the hole = Area of the hole x Depth of the hole
- Area of circular hole = π/4 x (dia)2 (π= 3.14)
- Volume = π/4 x (dia)2 x depth of hole
Step 4 Deduct the volume of the post from the volume of the hole
For 6 inch post, 18-inch hole and 24-inch deep, the volume of the concrete is
= π/4x (182-62)x 24= 5430.86 cubic inch, (where 18 inch is dia of the hole and 6 inch is dia of the post
Convert cubic inch to cubic feet
- cubic feet = cubic inch/1728
- 5430.86/1728 = 3.14 cubic feet
Step 5 Choose the size of the cement bag
As per your suitability, you can choose 40lb, 50lb, 60lb, and 80lb bags. Different sizes of bags have different yields.
| Bags size | Yield |
| 40lb | 0.30 cubic feet |
| 50lb | 0.375 cubic feet |
| 60lb | 0.45 cubic feet |
| 80lb | 0.60 cubic feet |
Step-6 Calculate the number of bags required
Divide the volume of the hole as calculated by the yield of the chosen bag
e.g. if we use a 50lb size having a yield of 0.375 cubic feet, then no. of bags = 3.14/0.375= 8.38
So, we can say that for a 6-inch post, and 18-inch hole, 8 bags of cement of 50lb weight will be used.
How Many 40 lb Concrete Bags Per Fence Post Chart
| Concrete bag per fence post for 40 lb Bag | |||
| Depth | 3″ Post, 9″ hole | 4″ Post, 12″ hole | 6″ Post, 18″ hole |
| 10 | 1.00 | 2.00 | 4.00 |
| 12 | 1.00 | 2.00 | 5.00 |
| 14 | 2.00 | 3.00 | 6.00 |
| 16 | 2.00 | 3.00 | 7.00 |
| 18 | 2.00 | 4.00 | 8.00 |
| 20 | 2.00 | 4.00 | 9.00 |
| 22 | 3.00 | 4.00 | 10.00 |
| 24 | 3.00 | 5.00 | 11.00 |
| 26 | 3.00 | 5.00 | 11.00 |
| 28 | 3.00 | 6.00 | 12.00 |
| 30 | 3.00 | 6.00 | 13.00 |
| 32 | 4.00 | 6.00 | 14.00 |
| 34 | 4.00 | 7.00 | 15.00 |
| 36 | 4.00 | 7.00 | 16.00 |
| 38 | 4.00 | 7.00 | 17.00 |
| 40 | 4.00 | 8.00 | 18.00 |
How Many 50 lb Concrete Bags Per Fence Post Chart
| Concrete bag per fence post for 50 lb Bag | |||
| Depth | 3″ Post, 9″ hole | 4″ Post, 12″ hole | 6″ Post, 18″ hole |
| 10 | 1.00 | 2.00 | 4.00 |
| 12 | 1.00 | 2.00 | 4.00 |
| 14 | 1.00 | 2.00 | 5.00 |
| 16 | 2.00 | 3.00 | 6.00 |
| 18 | 2.00 | 3.00 | 6.00 |
| 20 | 2.00 | 3.00 | 7.00 |
| 22 | 2.00 | 4.00 | 8.00 |
| 24 | 2.00 | 4.00 | 8.00 |
| 26 | 2.00 | 4.00 | 9.00 |
| 28 | 3.00 | 4.00 | 10.00 |
| 30 | 3.00 | 5.00 | 11.00 |
| 32 | 3.00 | 5.00 | 11.00 |
| 34 | 3.00 | 5.00 | 12.00 |
| 36 | 3.00 | 6.00 | 13.00 |
| 38 | 3.00 | 6.00 | 13.00 |
| 40 | 4.00 | 6.00 | 14.00 |
How Many 60 lb Concrete Bags Per Fence Post Chartsds
| Concrete bag per fence post for 60 lb Bag | |||
| Depth | 3″ Post, 9″ hole | 4″ Post, 12″ hole | 6″ Post, 18″ hole |
| 10 | 1.00 | 1.00 | 3.00 |
| 12 | 2.00 | 2.00 | 4.00 |
| 14 | 2.00 | 2.00 | 4.00 |
| 16 | 2.00 | 2.00 | 5.00 |
| 18 | 2.00 | 2.00 | 5.00 |
| 20 | 3.00 | 3.00 | 6.00 |
| 22 | 3.00 | 3.00 | 7.00 |
| 24 | 3.00 | 3.00 | 7.00 |
| 26 | 3.00 | 3.00 | 8.00 |
| 28 | 4.00 | 4.00 | 8.00 |
| 30 | 4.00 | 4.00 | 9.00 |
| 32 | 4.00 | 4.00 | 9.00 |
| 34 | 5.00 | 5.00 | 10.00 |
| 36 | 5.00 | 5.00 | 11.00 |
| 38 | 5.00 | 5.00 | 11.00 |
| 40 | 5.00 | 5.00 | 12.00 |
Also Read: