Post Hole Concrete Calculator
A post hole concrete calculator finds the concrete for setting fence or deck posts. It treats each hole as a cylinder, subtracts the post itself, and totals the bags across all your holes. Enter the hole diameter, depth, post size and number of holes below to get the bag count.
- Per hole
- 1.751 cu ft
- Total concrete
- 1.751 cu ft (0.0648 cu yd)
- 60 lb bags
- 4
- 50 lb bags
- 5
About 3 of the 80 lb concrete bags for 1 post hole.
How Much Concrete Do You Need per Post Hole?
To calculate concrete per post hole, find the volume of the cylindrical hole (pi times the radius squared times the depth), then subtract the volume the post itself displaces. A typical 12 inch diameter hole 30 inches deep holds about 2 cubic feet, and a 4x4 post in it takes up about 0.2, leaving roughly 1.8 cubic feet of concrete. That is about 3 of the 80 lb bags per hole. The calculator scales by the number of holes you enter.
How Deep and Wide Should a Post Hole Be?
A post hole is typically about three times the post width across, and roughly one third of the post height deep, with a minimum below your local frost line. A 6 ft tall 4x4 fence post is often set 2 to 3 ft deep in a 12 inch wide hole. Deeper, wider holes use more concrete, which the calculator factors in. Confirm against your local building code for fences and structural posts.
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Frequently asked questions
- How many 80 lb bags of concrete per fence post?
- A typical 12 inch diameter, 30 inch deep hole with a 4x4 post takes about 3 of the 80 lb bags. Deeper or wider holes raise this quickly.
- How do I calculate concrete for post holes?
- Find the hole volume (cylinder formula), subtract the post volume to depth, multiply by the number of holes. The calculator does this and converts to bag counts.