Fence Post Concrete Calculator
Calculate **concrete needed** for fence post holes with volume and bag count. **Concrete calculator** for post footings with displacement calculations.
Formula & Explanation
Concrete volume for each post hole is calculated as a cylinder minus the post volume: Hole volume = π × r² × depth - Where r = hole_diameter_inches ÷ 24 (convert to feet) Post volume = post_width² × depth - Post approximated as a square prism Net concrete per hole = hole_volume - post_volume Total concrete = concrete_per_hole × number_of_posts Bags (80 lb) = ceil(total_concrete ÷ 0.6) - One 80 lb bag of concrete yields approximately 0.6 cubic feet Waste percentage accounts for spillage, uneven holes, and over-ordering.
Assumptions
- •One-time calculation per fence project (not recurring)
- •Post holes are cylindrical (round holes have minimum volume)
- •Concrete yields approximately 0.6 cuft per 80 lb bag (standard)
- •Post is approximated as a square prism for volume displacement
- •Hole depth is measured from ground level to bottom (not including above-ground height)
- •Waste percentage 5-10% for typical installation (add more for uneven terrain)
- •Does not include reinforcement rebar, wire mesh, or concrete sealer
Example Calculation
A 100-foot fence with 14 posts (8-foot spacing) and 12-inch diameter holes at 2.5-foot depth requires 1.24 cubic feet of concrete per hole. Total: 17.36 cubic feet (0.64 cubic yards) or approximately 30 bags of concrete. With 10% waste, order 33 bags.
Inputs
Results
Common Post Hole Specifications
| postType | holeSize | depth | concrete |
|---|---|---|---|
| 4×4 | 12" diameter | 2-2.5 ft | 1.2-1.5 cuft |
| 4×4 | 12" diameter | 3 ft | 1.5-1.8 cuft |
| 6×6 | 18" diameter | 2.5 ft | 2.0-2.5 cuft |
| 6×6 | 18" diameter | 3 ft | 2.5-3.0 cuft |
Frequently Asked Questions
Related Calculators
Fence Calculator
Calculate exact **fence materials** needed including posts, pickets, rails, and concrete. Comprehensive **fence calculator** for complete project planning with the fencepost problem solver.
Fence Post Calculator
Determine **how many fence posts** you need with recommended hole depth and spacing. **Fence post calculator** solving the classic fencepost problem.
Concrete Calculator
Multi-purpose concrete volume calculator for slabs, footings, columns, and walls.
Concrete Footing Calculator
Calculate concrete volume and bag requirements for fence posts, deck footings, and pier foundations.
Deck Post Calculator
Calculate the number and size of posts needed for deck support based on deck dimensions and height.