Size of Adjacent Fence Posts

• Standard wooden picket fences and privacy fences typically are constructed with 4-by-4-inch weather-resistant lumber or pressure-treated posts. The 4-by-4-inch lumber typically is sufficient to support walk-through gates for these fences. Using the same size posts to build the fence and to support the gate lends visual continuity to the structure. If the gate is especially large or heavy, such as one built as a driveway gate, 6-by-6-inch posts should be used to construct the gate.
  
  

Standard Installation Depth

• The length of the gate post includes the length of the exposed above-ground portion of the post plus the buried portion. Fence posts typically are 33 percent longer than the height of the fence so that one-fourth of the post is buried underground. Because gateposts must endure more lateral stress than fence posts, the overall length of the gatepost typically is 50 percent longer than the above-ground height of the post. This allows one-third of the post to be buried underground.
  
  

Climate

• Regional climate must be considered to determine the required burial depth of fence posts and gate posts. If you live in a region where the ground freezes, the bottom of the posts must be buried below the frost line or else frost heave may occur, causing the post to be pushed out of the ground when the soil contracts with freezing temperatures. Contact your local building code officer to find out if there are recommendations or requirements for post burial depth.
  
  

Calculate Post Length

• To calculate the overall length of the gate post, begin with the desired above-ground height. Add to that dimension the length of the post that must be buried, according to the building code officer. Recalculate the overall length of the post by multiplying the above-ground height of the post by 1.5. Compare the products of both calculations. Select the larger of the two products to determine the overall length of the post.