Post Hole & Sonotube Calculator
Concrete and bags for fence posts, deck footings and sonotube piers.
Post hole concrete calculator
For deck footings, fence posts and sonotube piers. Includes 10% waste.
Concrete for all holes
0.38 yd³
2.59 ft³ per hole
Bags of concrete (rounded up)
18
80 lb
24
60 lb
28
50 lb
35
40 lb
Concrete for post holes & piers
Each hole is a cylinder, so the concrete depends on its diameter and depth. Enter both plus the number of holes and the calculator totals the volume and rounds bags up for every size. For a set-and-forget fence, a fast-setting mix poured dry into the hole is common.
Prices updated January 2026 National US averages · reviewed quarterly
Volumes use standard bag yields and a 10% waste allowance; costs are national US averages that vary by region, mix and finish. See our methodology for exactly how each figure is worked out, or check the reference sources:
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Frequently asked questions
How much concrete for a post hole?
A hole is a cylinder: π × radius² × depth. A 12" diameter hole 36" deep holds about 2.4 ft³ (0.09 yd³) — roughly 4 × 80 lb bags. The calculator totals it across all your holes with 10% waste.
How many bags of concrete per fence post?
For a common 8–10" diameter, 24–30" deep hole, plan on about 1–2 × 80 lb bags per post. Wider or deeper holes need more — enter your dimensions for the exact count.
What is a sonotube?
A cardboard forming tube for casting cylindrical concrete piers and footings. Its diameter is the hole diameter you enter here.