Fence Post Calculator
Count fence posts and the concrete to set them.
Enter your fence length and post spacing to get the number of posts, plus the concrete needed to set them based on your hole size. The concrete estimate subtracts the volume the post itself takes up in each hole.
How it works
Posts equal the number of spans plus one. Concrete per hole is the hole volume (π × radius² × depth) minus the post's volume, totaled across all posts and converted to 80-lb bags. A good rule is to bury about one-third of the post's height.
Frequently asked questions
How many fence posts do I need?
Divide the fence length by the post spacing and add one. A 100-ft fence with 8-ft spacing needs about 14 posts.
How deep should fence post holes be?
About one-third of the post's above-ground height, commonly 24–36 inches, and below your local frost line.
How much concrete per fence post?
It's the hole volume minus the post. A 10-inch-wide, 24-inch-deep hole around a 4-inch post takes a little under 1 cubic foot — roughly one to two 80-lb bags each.
How many bags of concrete per fence post?
Usually one to two 80-lb bags per post. A typical 10-inch-wide, 24-inch-deep hole around a 4×4 post takes a little under 1 cubic foot of concrete — about one and a half 80-lb bags.
Is this calculator free and private?
Yes. Every CubicCabin calculator runs entirely in your browser, so the numbers you enter are never uploaded or stored. There's no sign-up, no limits, and it keeps working even if you lose connection after the page loads.