The amount of concrete needed per fence post depends mainly on the size (diameter and depth) of the post hole and the post itself. Here are key points to consider:

• Most fence posts require between 1 to 10 bags of concrete, depending on the hole size and depth

• A typical guideline is that the hole diameter should be about three times the diameter of the post, and the hole depth should be about one-third to one-half the length of the post

• For example, a 12-inch diameter hole that is 24 to 30 inches deep (common for 4x4 posts) generally requires about 1 to 2 bags of concrete per post if using 50-pound bags

• Smaller holes (e.g., 8-10 inches diameter and around 18-24 inches deep) may need about 1 bag or less per post, while very large holes (e.g., 8 feet deep or 12-inch diameter for taller fences) can require up to 10 bags

• The volume of concrete needed is calculated by subtracting the volume of the post and any gravel at the bottom of the hole from the total hole volume

• For practical purposes, many DIYers use about 1 to 2 bags of 50-pound concrete mix per fence post hole of standard size (around 12 inches diameter and 24-30 inches deep)

• Using fast-setting concrete is often recommended to speed up the installation process

In summary, for a standard 4x4 wooden fence post with a 12-inch diameter hole about 2 to 2.5 feet deep, expect to use approximately 1 to 2 bags of 50-pound concrete mix per post. Larger or deeper holes will require more bags accordingly. Adjust based on your specific post size, hole dimensions, and soil conditions. References: