Free Fence Post Calculator — Posts & Concrete (2026)

How to Use This Calculator

1. 1Measure the total fence length along your property line in feet.
2. 2Enter the post spacing — 8 feet is standard, 6 feet for tall fences or high-wind areas.
3. 3Enter the post length — use 8-foot posts for a 6-foot fence (2 feet buried).
4. 4Click Calculate to get post count, concrete bags, and gravel needed.

About This Material

Fence posts are the foundation of any fence — they bear the full weight of the fence and resist wind forces that can exceed 20 pounds per square foot during storms. Choosing the right posts and setting them properly determines whether your fence lasts 5 years or 25 years. Standard residential fence posts are 4x4 pressure-treated lumber (3.5 x 3.5 inches actual). For a 6-foot privacy fence, use 8-foot posts with 24 inches buried in concrete. Gate posts and corner posts should be upgraded to 6x6 lumber (5.5 x 5.5 inches actual) because they bear significantly more lateral stress than line posts. Pressure treatment level matters for buried posts. Look for posts rated UC4A (ground contact) or UC4B (ground contact, heavy duty) — these resist decay in direct soil contact for 15 to 25 years. Posts labeled UC3B (above ground, exterior) will rot within 3 to 5 years if buried. Standard treated 4x4x8 posts cost $8 to $15 each. Cedar posts run $20 to $35 each. Metal post brackets ($15 to $30 each) allow mounting a wood post above ground on a concrete footing, eliminating wood-to-soil contact. Concrete is essential for post stability. Each standard post hole (10 inches diameter, 24 inches deep) requires approximately 2 bags of 50 lb pre-mixed concrete. Fast-setting concrete is popular for fence posts because it sets in 20 to 40 minutes. For each post, place 4 to 6 inches of gravel at the bottom of the hole for drainage so water does not pool around the base and accelerate rot. Post hole dimensions follow the rule of 3: the hole diameter should be 3 times the post width (10 to 12 inches for a 4x4 post) and the depth should be one-third the total post length plus 6 inches for gravel. In cold climates, post holes must extend below the frost line.

Installation Tips

• •Always call 811 before digging — hitting a buried utility line can be fatal and results in costly repairs.
• •Rent a two-person power auger for more than 5 post holes — it saves hours of labor.
• •Crown the concrete slightly above ground level and slope it away from the post so water drains away.
• •Use a post level to check plumb on two sides simultaneously while the concrete sets.
• •For gate posts, set them an extra 6 inches deeper and use 6x6 posts for extra strength.

Common Mistakes to Avoid

• ⚠Using posts not rated for ground contact — UC3B posts rot in 3 to 5 years underground.
• ⚠Skipping the gravel base — without drainage gravel, water pools at the post base and accelerates rot.
• ⚠Not mixing enough concrete — under-filled post holes allow the post to wobble and lean.
• ⚠Setting posts on a hot day without working quickly — fast-set concrete can begin hardening before you get the post plumbed.
• ⚠Forgetting to account for gates — each gate opening needs 2 extra posts with clearance for hinges and latch hardware.

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