How to Calculate How Much Concrete You Need for Fence Posts

There are a lot of factors that go into determining how much concrete you will need for fence posts. The factors include the height and width of the post, as well as how many posts you have in total.

If your soil doesn’t compact as hard as concrete, you should surround your fence posts with concrete to keep them firm. But how much? What kind? Do you want to show concrete footings under each post? It doesn’t matter if your fence is galvanized pipe, vinyl, or wood – securing your posts is the key to a long-lasting installation that will look great for years. In this blog post, we will walk through an example problem to help illustrate these concepts!


The depth at which fence post holes must be dug depends on the maximum depth of frost in winter. Fence post holes can be as little as two feet to the south or six feet or more to the north. For information on hole depth, contact your local building and code department. You will need to consult them for all necessary permits, so get information early.

Frost will cause posts to be lifted if the post footings are not below the frost line. This is the reason posts sink so deep in some regions. Even if you don’t have frost depth, you should still lower posts to half their height. A six-foot post should be nine feet long, three feet of which is in the ground. For very deep foundations, sometimes the post is only partially set in the hole, with the bottom of the hole filled with concrete.

Dig six-inch diameter holes for two-inch galvanized pipe posts. For optimum holding power, drill 8- to 12-inch-diameter holes for 4-by-4 posts.

Different types of concrete

You can order ready-mix concrete, usually in one cubic meter increments. You will need a few fence posts to use up a whole cubic meter of concrete. The driver will be in a hurry to get the concrete off his truck before it goes down. Plan to invite friends to help and have two or more concrete wheelbarrow to get it done quickly.

You can mix it in a wheelbarrow or a mixing trough. Ready to mix concrete is sold in 40, 50, 60, 70, and 80-pound bags. Just add water, mix thoroughly and pour. These two methods provide the strongest and longest-lasting concrete.

–°oncrete mix is poured directly into the hole, and water is added. In a short time, the concrete sets and holds the post in place. This type of mix does a good job of holding the post in place for a number of years before it begins to break down. However, they are more expensive than standard mixes.

Concrete Volume Facts

Every 40 pounds of unmixed concrete yields 0, 3 cubic feet of mixed concrete.

Two-inch diameter posts set in six-inch diameter holes require a 40-pound bag for every 24 inches of depth. You’ll have some leftovers to pour into the next hole.

4 x 4 posts set in 10-inch diameter holes will require a little more than three 40-pound bags for every 24 inches of depth. If you leave a little room for dirt to plant grass, three bags for each hole will be perfect.

If you order ready-mix concrete, remember that a yard will set about 30 – 4 x 4 fence posts in 10-inch diameter, two-foot deep holes.

1 cubic yard =27 cubic feet. A 4 x 4 post in a 10-inch diameter x 24-inch deep hole requires 0, 92 cubic feet of concrete to fill the hole. 27 cu feet / 0, 92 cu feet =29, 3 holes. If you leave a little out of each hole to fill with dirt, you can fill 30 holes.

One yard of concrete requires six to eight heavy wheelbarrow loads, depending on the size of the wheelbarrow.