Hole Diameter and Depth Guidelines
Post hole sizing depends on post size, soil type, and the load above. A common approach is to make the hole 3 times the width of the post. For example, a 4x4 post often uses a 12-inch hole. Depth is usually one-third of the post length plus a few inches of gravel for drainage. In freeze-prone areas, the bottom of the hole must extend below the frost line to prevent heaving.
Concrete per Post and Total Volume
The concrete per post hole is based on the volume of a cylinder. The post hole calculator above estimates cubic yards per hole and total volume for multiple holes. For irregular holes or belled bottoms, add extra concrete to cover flare and sloughing. Ordering an extra 5–15% prevents running short during the set.
Setting Tips
Compact the soil at the bottom, add a few inches of gravel, and check that posts are plumb before the concrete sets. For fence posts, brace each post until the concrete has firmed up. Avoid disturbing the post for at least 24 hours. For gates or heavy loads, wait longer before attaching hardware.
Frequently Asked Questions
How deep should a post hole be?+
A common rule is one-third of the post length in the ground, plus a few inches for gravel. Frost depth may require deeper holes.
How wide should a post hole be?+
Most holes are 3x the post width in diameter. Wider holes provide better stability, especially in loose soil.
How much concrete per post?+
It depends on hole diameter and depth. Use the post hole calculator to estimate cubic yards per hole and total volume.
Should I use gravel at the bottom?+
Yes. A few inches of gravel improves drainage and reduces moisture around the post base.
Can I set posts without concrete?+
Gravel-set posts work in some climates, but concrete is more stable and durable for fences, decks, and gates.
How long should I wait before loading a post?+
Allow at least 24–48 hours for light loads and longer for heavy gates or structures. Full cure takes about 28 days.
Related Calculators
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