• Line posts are typically 36 inches deep.fence image by Brett Bouwer from Fotolia.com
  
  

36 to 48 Inches Deep is Typical

• According to Penn State Agricultural Research and Cooperative Extension, 36 inches is the typical fence post depth for line posts. Fences in areas with very sandy or wet soil will need posts more deeply set. Gate posts and corner posts, which are often larger and under more strain, are typically driven to a depth of 48 inches.
  
  

Relate Depth to Post Diameter and Soil Type

• According to Mississippi State University Extension Service, the depths of the posts should be related to their diameter and the soil type. In loose, sandy soils, they recommend a post depth 15 times that of the post diameter. In medium to heavy clay soils, they recommend sinking the post to a depth 10 times greater than the diameter of the post. For example, a 4-inch diameter post in heavy clay soil would be sunk to a depth of 40 inches.
  
  

Bottom Line

• While 36 inches for line posts and 48 inches for corner posts and gate posts are good rules of thumb, all factors must be considered. Soil type, the size of the fence posts, and the type of fence should all be taken into account to ensure that the posts are set solidly.