Dig the hole using the post hole diggers to about 2 feet 4 inches. Heres a general guide. Fence Depth Post Holefence Post Hole Depth Wood Fence Post Fence Design Building A Fence The hole depth should be below the frost line. How deep to dig fence post . The deeper you dig the holes the more stability your fence has so youd better purchase some longer posts. Today were going over how to calculate the depth of your fences post holes before you start digging. You could dig it out but that takes too long. Measure and mark the location of each fence post. So if youre installing a 6-foot tall fence your post hole should be at least two feet deep. If you dont want to dig fence posts 2 Id recommend a portable fence option. As a general rule of thumb one-third of your post should be underground the other two-thirds above. You need to dig a 12-inch wide hole for a 4-foot wood post. Youll also want to be sure the bottom of the post sits below the frost line. The de...