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Post Hole Concrete Calculator
How much concrete per post hole? Enter diameter, depth and hole count: get total yards and bags instantly.
Estimates only. Bag yields per manufacturer specs (80 lb ≈ 0.60 ft³, 60 lb ≈ 0.45 ft³, 40 lb ≈ 0.30 ft³). Ready-mix trucks carry ≈ 10 yd³. Always round up and confirm with your supplier.
Eight fence post holes at 10 inches wide and 36 inches deep need about 13 cubic feet of concrete, roughly 22 bags of 80 lb mix. The free post hole concrete calculator below totals any number of holes so you buy the right number of bags first time.
How to use the post hole concrete calculator
- Measure the hole diameter in inches.
- Enter the hole depth in inches.
- Enter the number of holes.
- Read the total: cubic feet, cubic yards and bag counts for 40, 60 and 80 lb bags.
Formula
Each hole = π × radius² × depth. Total = one hole × number of holes.
Practical tips
- Make holes 3 times the post width: a 4 in post needs a 12 in hole.
- Depth should be half the above-ground post height, minimum 24 inches for fences.
- Gravel at the hole bottom improves drainage around the post.
- Set posts with a slight concrete dome above ground so water runs off.
Frequently asked questions
How many bags of concrete per fence post?
A standard 10 in by 36 in hole needs 3 bags of 80 lb concrete. Smaller 8 in holes need 2 bags.
Should the whole hole be concrete?
Fill the bottom 6 inches with gravel for drainage, then concrete to just above ground level.
How deep for a 6 ft fence post?
Bury one third of the post: 36 inches deep for a 6 ft fence is the safe rule.
See the full concrete calculator or convert any volume with the bag calculator.
Worked examples
Example 1: 8 holes, 10 in dia, 36 in deep. Total = 0.48 cubic yards. With 10% waste: 24 x 80 lb bags.
Example 2: 20 fence holes, 12 in dia, 36 in deep. Total = 1.75 cubic yards. With 10% waste: 87 x 80 lb bags.
Post hole reference table
Per hole, 80 lb bags, no waste.
| Hole size | Cubic yards | Bags per hole |
|---|---|---|
| 8 in dia x 24 in | 0.03 | 2 |
| 10 in dia x 36 in | 0.06 | 3 |
| 12 in dia x 36 in | 0.09 | 4 |
| 12 in dia x 48 in | 0.12 | 6 |
More post hole questions
How many bags per fence post hole?
A 10 in diameter hole 36 in deep takes 3 x 80 lb bags.
How deep should fence post holes be?
One-third of the post length underground, minimum 24 inches. In frost areas, go below the frost line.