Fence Post Concrete Calculator
Enter your fence length and maximum post spacing. PlanDIYBuild estimates the posts, subtracts post displacement from each round hole, accounts for drainage gravel, and gives concrete per post plus whole 40, 50, 60 and 80 lb bag quantities.
Fence post concrete
See how total fence length, maximum post spacing, actual post width, total post-hole depth, post-hole diameter, drainage gravel depth and concrete extra / waste define the post count and concrete quantity.
Start with the essentials
Enter the total fence length and the farthest apart you want the posts. PlanDIYBuild estimates the post count and concrete using practical post-hole defaults you can adjust below.
CUSTOMIZE PROJECT DETAILSAdjust assumptions & product details+
Check the method or common questions
Method, formula & assumptions
Fence post concrete planning
Formula: PlanDIYBuild divides the fence run into equal bays no longer than your maximum spacing, adds one post, then calculates the round concrete zone for every hole. It subtracts the square post volume, excludes the selected drainage-gravel depth, adds your extra-material allowance and rounds common concrete bag sizes up to whole bags.
Worked example: Example: an 80 ft straight fence with an 8 ft maximum spacing creates 10 bays and 11 posts. With the default 12 in holes, 36 in total depth, 6 in gravel layer and a 3.5 in square post, the calculator subtracts the post displacement before converting the remaining concrete volume to whole bags.
Before you buy: Post spacing, hole diameter, embedment depth, drainage detail and concrete requirements depend on fence height, wind exposure, frost depth, soil, post material, gate loads and local requirements. The defaults are planning assumptions, not a structural or code prescription.
Fence Post Concrete Calculator FAQ
How many bags of concrete do I need per fence post?
It depends on the hole diameter and concrete fill depth, plus the space displaced by the post. Enter your fence length and spacing for the full project, then adjust the hole and post dimensions to match your plan.
Does the calculator subtract the fence post from the concrete volume?
Yes. It calculates the round concrete zone and subtracts the volume occupied by the square post through that concrete depth.
Does gravel at the bottom reduce the concrete needed?
Yes. The selected drainage-gravel depth is excluded from the concrete fill depth and estimated separately. Verify whether gravel is appropriate for your post-setting detail and site conditions.
Which bag size should I buy?
The calculator shows 40, 50, 60 and 80 lb bag equivalents. These are alternatives, not quantities to add together. Verify the yield printed on the exact concrete mix you purchase.
How does PlanDIYBuild determine the number of fence posts?
It rounds the number of fence bays up so no calculated bay exceeds your selected maximum spacing, then adds one post for a straight run. Corners, gates and separate runs can require additional posts; use the full Fence Calculator for those layouts.
Continue your Fence project
Use the Fence planning hub for related calculators and quick-reference guides.
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