Post Hole Concrete Calculator
Enter the hole diameter, depth, and how many holes you are digging, and this post hole concrete calculator gives the concrete volume in cubic feet — converted into rounded-up 60-lb and 80-lb bag counts.
A 60-lb bag yields about 0.45 cu ft; an 80-lb bag about 0.6 cu ft. Counts round up.
Estimates only — not financial advice. This calculator gives approximate figures for planning. It is not financial, tax, or legal advice; check with a qualified professional before making decisions.
How the post hole concrete calculator works
Each hole is a cylinder: π times the radius squared times the depth. The diameter in inches becomes a radius in feet by dividing by 24 (half of 12), the depth in inches becomes feet by dividing by 12, and multiplying gives the cubic feet of concrete one hole swallows.
Bag counts come from real yields: a 60-lb bag of mix makes about 0.45 cubic feet of set concrete, an 80-lb bag about 0.6. Dividing the total volume by the yield and rounding up guarantees you do not come up one bag short mid-project.
V = π × (d/24)² × (h/12) · bags60 = ⌈V / 0.45⌉ · bags80 = ⌈V / 0.6⌉
Related tools
Keep exploring: Fence Post Depth Calculator · Concrete Cubic Yard Calculator · Gravel Calculator.
Post hole concrete calculator FAQ
How much concrete do I need per post hole?
A 10-inch-diameter hole 24 inches deep holds about 1.09 cu ft — roughly two and a half 60-lb bags. Bigger holes scale fast: a 12-inch hole at the same depth needs about 1.57 cu ft.
60-lb vs 80-lb bags: which should I buy?
Either — the concrete is the same. A 60-lb bag yields ~0.45 cu ft and an 80-lb bag ~0.6 cu ft, so you need about 25% fewer 80-lb bags; they are just heavier to carry.
Dry-set or wet-set concrete for posts?
Wet-set (mix with water, pour, set the post) gives the strongest, most consistent result. Dry-set (pour dry mix, add water on top) is faster but can leave dry pockets in deep holes.
How wide should a post hole be vs the post?
About three times the post width: a 4×4 post (3.5 in actual) wants a 10–12 inch hole. Wider holes in loose soil need more concrete — measure the actual dug hole, not the ideal.
How deep should a fence post hole be?
One-third of the post’s above-ground height, minimum — so a 6 ft fence wants 2 ft in the ground. Below the local frost line is the rule where the ground freezes.