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, applies a visible editable field allowance, and converts the order 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
Choose a field allowance
Set a visible buffer for irregular excavation, sloughing, spillage, and placement variation. The 10% starting value follows published Sakrete estimating guidance, but remains editable and is not a universal code or project requirement.
- 05
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, have about 11.94 cubic feet of net geometry. A visible 10% field allowance makes the order volume about 13.14 cubic feet, which rounds up to 22 eighty-pound bags at the editable 0.60-cubic-foot yield, 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.
Scope and safety note
Material-volume estimate only. The 10% starting allowance follows cited manufacturer estimating guidance but remains an editable planning buffer, not a code or universal project requirement. Hole diameter, embedment, reinforcement, frost protection, drainage, and post setting details are site- and system-specific. Contact the applicable 811 center, locate utilities, and confirm local requirements before excavation.
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 and test check recorded July 17, 2026. What this review covers
Formula version 2026-07-17.1
No named qualified reviewer is recorded for this calculator. Treat the result as planning support and obtain the professional or code review identified in its safety note.
- Call 811 - contact your local utility-notification center before digging (opens in a new tab)
Supports the utility-locate warning. State notice periods and excavation rules vary; this source does not prescribe post-hole dimensions.
- QUIKRETE Concrete Mix product data (opens in a new tab)
Supports the selectable 40, 50, 60, and 80 lb nominal bag yields. The selected product label remains controlling.
- Sakrete - Concrete Calculators (opens in a new tab)
Supports 10% as the initial field-allowance value for concrete estimates, including post setting. It is editable planning guidance, not a universal code or product requirement.
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, the editable field allowance, and the actual bag yield. The result divides the order volume 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.