Enter your Post Diameter, Hole Diameter, Post Depth, and Hole Depth to find how many concrete bags you need — the Post Hole Concrete Calculator subtracts the post volume from the hole volume across your Number of Posts, giving you Bags Per Hole, Total Volume, and Total Bags Needed based on your bag size.
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Yes, dry concrete mix can be poured directly into the post hole around the post, then water is added. This is called the dry-pour method and works well for fence posts, though mixing concrete first provides stronger results.
For a 4x4 fence post, dig a hole that's 12 inches in diameter. The hole should be about 1/3 the length of the post deep, typically 24-30 inches for an 8-foot post.
Fence post holes should be at least 1/3 the total post length deep. For an 8-foot post, dig 24-30 inches deep. In areas with frost, go below the frost line, typically 36 inches or more.
Typically, you'll need 1-3 bags of concrete per post hole, depending on the post size and hole dimensions. A standard 4x4 post in a 12-inch diameter hole usually requires 1-2 bags of 50-lb concrete mix.
The main difference is the amount of concrete mix. An 80 lb bag covers about twice the volume of a 40 lb bag. Choose based on your project size and how much weight you can comfortably handle.
Yes, always buy 10-15% extra concrete bags. It's better to have extra bags than to run short during your project. Leftover bags can be stored for future repairs or other projects.
Fast-setting concrete typically sets in 20-40 minutes, while regular concrete mix takes 24-48 hours to fully cure. You can install the post immediately with fast-setting concrete but wait before adding fence panels.