The amount of concrete needed per fence post depends mainly on the size of the post hole and the diameter of the post itself. Here are the key points:
- For a typical 4x4 wooden post set in a 12-inch diameter hole about 30 inches deep, the volume of concrete needed is roughly 1.6 cubic feet, which translates to about 240 pounds of concrete or approximately 2 to 3 bags of 50-pound concrete mix per post
- The hole diameter is usually recommended to be about three times the diameter of the post. For example, a 4-inch post would have a 12-inch diameter hole, and the depth should be about 1/3 to 1/2 the length of the post
- Some experienced builders suggest that an 8-inch diameter hole (smaller than 12 inches) can be sufficient, requiring about 0.6 cubic feet or 90 pounds of concrete (about 1 to 2 bags per post), especially if the soil is stable and gravel is used at the bottom for drainage
- It's advisable to put about 4 to 6 inches of gravel at the bottom of the hole before pouring concrete to improve drainage and prevent frost heave
- For setting posts in typical soil conditions, 1 to 2 bags of concrete per post are common, but in sandy or loose soil, more concrete may be needed for stability
- Using too much concrete (like 4 bags or more per post) is often unnecessary and can make future post removal difficult
In summary, for a standard 4x4 fence post, expect to use about 1 to 3 bags of 50-pound concrete mix per post, depending on hole size, soil conditions, and fence height. Adjust hole diameter and depth accordingly, and always include gravel at the bottom for drainage. This approach balances stability with material efficiency.
