Fence Post and Concrete Calculator
Count posts from maximum spacing, then calculate the annular concrete volume around a centered square post inside each cylindrical hole.
What does the fence post calculator calculate?
Each equal fence run needs one more post than its rounded section count. Concrete volume equals cylindrical hole volume minus the embedded square-post volume, multiplied by all posts and waste. Divide by the bag’s stated mixed yield and round up. Gate, corner, frost, and structural footings may differ.
Fence post and hole-concrete formulas
Every independent run has two endpoints around its rounded sections. Concrete fills the cylindrical hole volume remaining after the embedded square post displaces material.
How to measure for an accurate estimate
- Measure each independent straight run from terminal-post center to terminal-post center.
- Use the approved maximum spacing and add separate corner, gate, brace, or transition posts to the final plan.
- Measure hole diameter and concrete-filled depth, distinguishing gravel bases or unfilled drainage zones.
- Use actual post width and the mixed cubic-foot yield printed for the exact bag size and concrete product.
Two equal 48-foot fence runs
Two 48-foot runs use 8-foot spacing, 12-inch holes 3 feet deep, 3.5-inch posts, 0.375-cubic-foot bags, and 10% waste.
Each run has six sections and seven posts; 14 posts need about 32.35 cubic feet of concrete with allowance, or 87 bags.Before you purchase material
- Arrange required utility locating and verify property boundaries, easements, setbacks, and permits before excavation.
- Have gate, corner, tall, solid, and high-wind fence posts and foundations designed for their larger loads.
- Use posts, concrete, coatings, and fasteners suitable for ground contact, soil chemistry, drainage, and exposure.
- Brace posts plumb and follow concrete manufacturer requirements for water, mixing, placement, cure, and loading.
Common questions
How deep should a fence post hole be?
Depth depends on fence height and solidity, post and footing design, soil, drainage, frost depth, wind, gates, and local code. A rule of thumb cannot replace local requirements. Gate and corner posts often need larger foundations.
Why subtract the post volume from concrete?
A centered post occupies part of the cylindrical hole, so concrete fills only the remaining space. The subtraction matters for large posts and many holes. Irregular excavation, soil collapse, voids, and overfilling still justify a field allowance.
How many concrete bags fill a post hole?
Calculate the hole’s remaining cubic volume, then divide by the mixed yield printed on the exact concrete bag. Bag weights have different yields. Round up and include allowance for uneven holes, spillage, and grade finishing.
Should every fence post use the same footing?
Not necessarily. Gate, corner, end, brace, tall, and wind-exposed posts can carry much larger loads than intermediate posts. Soil and frost conditions also vary. Use a locally appropriate design rather than applying one hole size everywhere automatically.
Sources and reference standards
- Call 811Official U.S. one-call resource for arranging underground utility marking before digging.