Post Hole Concrete Calculator

Use this tool to calculate the concrete your post-hole requires.

Hole depth2 ft2 ft — a third of the height, adjusted for soil and wind

Post length to buy8 ft8 ft

Hole diameter12 inthree times the post width

Concrete per post1.3963 cu ft3 bags of 80 lb mix

Concrete for all 14 posts0.724 yd³33 bags

Buried fraction25%

Gravel at the base0.2618 cu ft per posta 4 in layer, so the post foot can drain

The method

depth = one third of the height above ground, and at least 2 ft

A third down, and never less than two feet

A fence post is a lever: wind pushes on the panel and the soil has to resist the turning moment. Burying a third of the exposed height gives enough depth for the soil to do that, which is why a 6-foot fence wants 2 feet in the ground and an 8-foot fence wants nearly 3.

Two things override the arithmetic. In cold climates the hole must reach below the frost line, because water freezing under the footing will lift it — and once heaved, the post never goes back. Solid panels also catch far more wind than picket fences, so treat them as exposed even in a sheltered garden.

Put four inches of gravel in the bottom before the concrete. A post sitting in a concrete cup that holds water rots from the base up, whatever it is treated with.