Fence Post Depth Calculator
A fence is only as strong as its posts, and post depth is the most critical factor in long-term stability. This calculator determines the proper hole depth, diameter, and concrete quantity based on your fence height, post size, soil conditions, and wind exposure to ensure your fence stands firm for years.
The general rule for fence post depth is to bury one-third of the total post length underground, with a minimum depth of 24 inches. A 6-foot fence needs at least 30 inches of burial depth (24 inches of depth plus 6 inches of gravel base). Taller fences and high-wind areas require deeper holes.
Hole diameter should be approximately three times the post width. For a 4x4 post (3.5 inches actual), dig a 10-inch diameter hole. For a 6x6 post (5.5 inches actual), dig a 12-inch hole. This provides enough room for concrete to surround the post and resist lateral forces from wind loading.
Always place 6 inches of gravel at the bottom of the hole for drainage before setting the post. Crown the concrete slightly above grade and slope it away from the post to prevent water from pooling at the base. In cold climates, setting posts below the frost line prevents frost heave from shifting the fence.