What this estimate includes
This estimate shows concrete needed for post holes, including cubic feet, cubic yards, and common bag counts.
Before you order
Hole depth requirements vary by frost line, soil conditions, post load, and local code. Use this as a planning estimate and confirm requirements before digging or ordering.
Frequently Asked Questions
How much concrete do I need for fence posts?
A typical 6-inch diameter hole at 24 inches deep holds about 0.33 cubic feet of concrete -- roughly 1 bag of 40 lb or half a bag of 80 lb. For 10 posts at that size, you need about 3.3 cubic feet total, or 6 bags of 80 lb.
How deep should a post hole be?
A general rule is one-third of the post length should be in the ground, with a minimum of 24 inches below grade. In cold climates, holes must extend below the local frost depth -- check your local building code. Frost-prone areas typically need 36-48 inches.
How wide should a post hole be?
Post holes should be 3 times the width of the post. For a 4x4 post (3.5 inches actual), dig a 10-12 inch hole. For a 6x6 post (5.5 inches actual), dig a 16-18 inch hole. A wider base adds stability in soft soil.
How many bags of concrete per post?
For a standard 6-inch diameter x 24-inch deep hole, about 1 bag of 80 lb concrete fills the hole. For larger or deeper holes, use the calculator above. Always check manufacturer yield on the bag label.
Should fence posts be set in concrete?
Yes for most applications. Concrete holds posts firmly and prevents movement. For temporary fences, gravel-tamped posts are an option. Wood posts set in concrete can rot at the concrete line over time -- use pressure-treated lumber rated for ground contact.
How much extra concrete should I buy?
Add 10% to account for variation in hole diameter -- hand-dug holes are rarely perfectly cylindrical. For machine-bored holes, 5% extra is usually enough.
Can I use fast-setting concrete for posts?
Yes -- Quikrete Fast-Setting Concrete and similar products are designed for posts. Pour dry mix directly into the hole, add water on top, and it sets in 20-40 minutes. No mixing required. Yields are slightly lower per bag than standard concrete -- check the bag label.