Post Hole Concrete Calculator

Post hole concrete calculator for fence and deck posts. Enter diameter, depth, and hole count to estimate yardage and 80 lb bags. For cylindrical piers, use the sonotube calculator, and see the footing size guide for depth and diameter rules of thumb.

Inputs

Hole diameter (in)

Depth unit

Hole depth (in)

Number of holes

Waste (%)

Tip: Add extra depth for gravel at the bottom or below frost depth.

Results

Total volume

0.8 yd³

21.6 ft³

80-lb bags (rough)

36

Assumes ~0.6 ft³ yield per 80-lb bag (varies by mix).

FAQ

How much concrete for a 12" × 30" post hole? One hole is about 1.96 ft³; multiply by hole count and add waste.
Do I need gravel under fence posts? A few inches of gravel improves drainage and prevents rot.
How many 80-lb bags per post? Divide total cubic feet by 0.6 to estimate bags.

Assumptions

Holes are cylindrical with uniform diameter.
Waste accounts for spillage and irregular hole walls.
80-lb bag yield is an approximation; check product labels.

Example

10 holes at 12 in diameter and 30 in deep with 10% waste need about 0.8 yd³ of concrete.

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