Free estimate — verify against local code before building
Fence Post Hole Concrete Calculator
Estimate concrete bags and base gravel for round fence-post holes after subtracting the post itself.
What this calculator includes
Size the concrete that actually surrounds each post instead of treating the hole as solid concrete. This calculator subtracts the embedded square-post volume, keeps the gravel base separate, and converts the remaining volume into whole bags using an editable label yield.
How to use this fence post hole concrete calculator
- 01
Count and measure holes
Enter the number of equal round holes, their finished diameter, and total depth. Split different hole sizes into separate estimates.
- 02
Enter the post and gravel zone
Use the actual square-post width, below-grade post depth, and planned gravel-base depth. The calculator subtracts the post from only the concrete-filled height.
- 03
Match the concrete bag
Choose 40, 50, 60, or 80 lb mix and replace the planning yield with the volume printed on that product's label.
- 04
Check local depth requirements
Before digging, confirm utilities, frost depth, wind exposure, soil, gate loads, and the fence system's instructions with the local authority and installer.
Worked example
Example: ten 10-inch holes for 4-inch posts
Ten 10-inch-diameter holes, each 36 inches deep with a 4-inch post, 33-inch embedment, and 3-inch gravel base, require about 11.94 cubic feet of concrete. At the editable 0.60-cubic-foot yield, that rounds up to 20 eighty-pound bags, plus about 1.36 cubic feet of gravel or 3 half-cubic-foot bags.
Practical buying and overage guidance
Use one concrete product and the yield on its current bag. Buy enough full bags for the displayed rounded quantity, keep mix dry before use, and stage water and tools before opening bags. Confirm whether bulk concrete is more practical for a large fence line.
Calculation sources and review
Primary references and formula assumptions are linked so you can verify them against the selected product, supplier, and adopted local requirements.
Internal formula review completed July 13, 2026. What this review covers
- American Wood Council - Prescriptive Residential Wood Deck Construction Guide (opens in a new tab)
Illustrates why footing dimensions and frost protection come from the applicable design and local requirements, not a universal calculator preset.
- QUIKRETE Concrete Mix product data (opens in a new tab)
Manufacturer reference for checking bag-specific yield and placement instructions.
Frequently asked questions
Does the calculator subtract the fence post from the hole volume?
Yes. It calculates the round concrete envelope and subtracts the volume of the embedded square post. The gravel layer below the post is calculated separately.
How many concrete bags fit one post hole?
That depends on hole diameter, concrete height, post displacement, and the actual bag yield. The result divides the net cubic feet by the editable bag yield and rounds up to a whole bag.
Why can I edit the concrete yield?
Bag weights do not guarantee identical usable yield across every mix. Packaging and manufacturer data control, so the common planning value changes when you select a size and remains editable.
How deep should a fence post hole be?
There is no universal depth. Fence height, wind, soil, frost conditions, post material, gate loads, and local rules all matter. Confirm the system instructions and local frost-depth requirements before digging.
Is gravel always required under a fence post?
Not for every fence system or soil condition. The calculator can quantify an entered gravel layer, but the selected post and footing detail should decide whether it belongs in the installation.