How much concrete do I need for footings and post holes?

Post hole concrete reference table

Round cylindrical holes — the most common shape for deck and fence post footings. Bag counts use an 80 lb / 25 kg bag and are rounded up.

Volume = π × (diameter ÷ 2)² × depth. Bag counts rounded up. Add 5–10% for spillage on larger pours. Footing depth requirements vary by location and jurisdiction — check with your local building department.

Need the full working? Read the footing concrete guide →

Common questions

How many bags of concrete do I need for a post hole?

It depends on the hole size. A typical round post hole — 10 inches (250 mm) in diameter and 48 inches (1,200 mm) deep — holds about 2.18 cubic feet (0.062 m³) of concrete, which takes 4 bags of 80 lb premix or 6 bags of 25 kg metric mix. Use the calculator above for your exact hole dimensions.

How do you calculate concrete for a round post hole?

Volume = π × (diameter ÷ 2)² × depth. For a 10-inch-wide, 48-inch-deep hole: π × 5² × 48 = 3,769 cubic inches ÷ 1,728 = 2.18 cubic feet. Divide by the yield per bag (an 80 lb bag yields 0.60 ft³), round up: 2.18 ÷ 0.60 = 3.6 → 4 bags. The calculator above does this in one step for round, square and rectangular footings.

How deep should concrete footings be?

Footing depth must reach below the local frost line so freeze–thaw movement does not heave the post. Frost line depth varies by location — typically 12–18 inches in mild climates, 36–48 inches or more in cold regions like Canada and the northern United States. Always check with your local building department for the minimum depth required in your area; deck and structural post footings also need to meet your jurisdiction's code.

How much concrete do I need for 6 post holes?

Multiply the single-hole volume by 6. A 10-inch-diameter, 48-inch-deep hole uses about 2.18 ft³ of concrete, so 6 holes need 6 × 2.18 = 13.1 ft³ ≈ 0.48 cubic yards. At 0.60 ft³ per 80 lb bag, that is 22 bags. Enter '6' in the Number of footings field above for an instant total.