🕳️ Post Hole Calculator

How wide should a post hole be?
A common rule of thumb is to dig the hole three times the diameter of the post. For example, a 4-inch post should have a 12-inch hole, and a 6-inch post an 18-inch hole, providing enough concrete around the post for stability.

How deep should a post hole be?
Post holes are typically dug to 1/3 to 1/2 of the post height above ground, and should extend below your local frost line. A typical fence post hole is 24-30 inches deep; a deck post hole is 36-48 inches.

How many bags of concrete do I need per post hole?
It depends on the hole size. A typical 12-inch diameter by 24-inch deep hole needs about 1.5 bags of 80 lb concrete. Formula: Volume = π × (hole radius² - post radius²) × depth.

Why do I need a gravel layer?
A 4-6 inch gravel layer at the bottom improves drainage and prevents moisture from pooling and rotting the post. It is not counted as concrete volume but reduces the concrete you need.