DATUM

Fence Post Concrete Calculator

Concrete per post hole and total bags for a fence, with embedment depth checked against the one-third rule and a frost depth warning.

Fence Post Concrete Calculator

How much concrete per hole, how many bags for the whole fence, and how deep the hole should be — the depth rule is the part people skip and then rebuild.

grade above depth
Depth is what holds a fence up. Frost depth overrides any rule of thumb — a footing above the frost line will lift the post out of the ground over a winter.
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Concrete per hole—
Total concrete—
Bags needed—
Hole depth vs post height—
Post embedded—

Concrete per hole is the hole cylinder minus the post and minus the gravel base: π(d÷2)² × (depth − gravel) − post area × (depth − gravel). Bag yields are Quikrete's published figures (Technical Data Sheet #1101) — 80 lb yields 0.60 ft³, 60 lb yields 0.45 ft³.

A common rule of thumb puts roughly a third of the total post length in the ground, and hole diameter at about three times the post width. Frost depth overrides both: in a freezing climate the footing must extend below the local frost line or the post will heave, and that depth is set by your building department, not by a rule of thumb. Check it before you dig.