Digging 48-Inch Gate Post Holes by Hand for a 36-Inch Garden Gate: 12-Inch Diameter, a 6-Inch Gravel Base, and 40-1/2-Inch Post Centers

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Dig each hole 12 inches wide and 48 inches deep for an 8-foot 4x4, pour 6 inches of gravel, and set the posts 40-1/2 inches center to center. That leaves a 37-inch opening for a 36-inch gate.

How deep should gate post holes be for a garden gate?

Set gate posts at least one-third of their length in the ground, which is 32 inches for an 8-foot post, and the USDA NRCS minimum for 8-foot wood corner and gate posts is 3-1/2 feet. Dig to 48 inches to leave room for a 6-inch gravel base.

The Home Depot's gate building guide says gate posts should be set about one-third of their length deep and anchored in concrete, with a hole depth of at least that. It also gives a 1/2 to 3/4 inch latch gap and about 1/4 inch on the hinge side for 4x4 posts.

The USDA NRCS Nebraska fence practice specification lists wood corner and gate posts at a minimum of 8 feet long with 3-1/2 feet in the ground.

Hole Depth Math for an 8-Foot Post

Item Measurement How it is figured
One-third rule 32 in. 96 in. divided by 3
NRCS minimum in ground 42 in. 3-1/2 ft. x 12
Gravel base 6 in. Drainage under the post
Hole depth to dig 48 in. 42 in. plus 6 in.
Post above ground 54 in. 96 in. minus 42 in.

Materials and Tools

  • Post hole digger with a long handle
  • Two 8-foot pressure-treated 4x4 posts
  • About 0.8 cubic foot of gravel and 6 bags of 60-pound concrete mix
  • A level, string, tape measure, and 2x4 braces with stakes
  • Gloves and a digging bar for stones

Digging and Setting Steps

  1. Set the spacing. For a 36-inch gate add 1/2 to 3/4 inch at the latch and 1/4 inch at the hinge, giving a 37-inch clear opening.
  2. Find the centers. A 4x4 is 3-1/2 inches wide, so the posts sit 40-1/2 inches apart on center.
  3. Start the hole. Mark a 12-inch circle and lift out the sod first.
  4. Dig in lifts. Open the blades, push down, close, and lift, clearing about 12 inches per pass.
  5. Keep the walls straight. Check the diameter every foot so the hole does not taper.
  6. Reach 48 inches. Measure from ground level, not from the pile.
  7. Add gravel. Tamp 6 inches in the bottom.
  8. Set and plumb. Brace the post on two sides and check both faces with the level.
  9. Pour. Fill with concrete, slope the top away from the post, and let it cure 24 to 48 hours.

Each hole holds about 3.1 cubic feet, and after the gravel and the post you need about 2.5 cubic feet of concrete. A 60-pound bag yields about 0.45 cubic foot, so plan 6 bags for two holes.

Hole Problems

  • A hole wider than 12 inches wastes concrete and does not add much strength
  • Water pooling in the hole means the gravel base is too thin
  • Rocks stop the digger, so break them with a digging bar
  • Mark the post height before you set it, because you cannot lower it later

A garden gate frame is the next step, and a T-post and cattle-panel arch trellis over a raised-bed path is a good use for the entry. Wire fence tied into these posts is explained in setting an 8-foot T-post deer fence around a vegetable garden. The hardware cloth mesh size and gauge guide covers the lower mesh to add along a gate.

Posts that lean over winter can be fixed as in pulling and resetting frost-heaved T-posts.

FAQ

Do I have to use concrete?

Gate posts carry swinging loads, so concrete is the safer choice.

How long before I hang the gate?

Wait for the concrete to cure, at least 48 hours.

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