Fence Post Concrete Calculator
Updated Formulas shown
A typical 4×4 post in a 10-inch hole, 30 inches deep, takes about 3 bags of 50 lb (or 2 bags of 80 lb). Fast-setting mixes have the same yield per pound; a narrower 8 in hole cuts that roughly in half.
- 50 lb bags
- 310.375 ft³ each
- 80 lb bags
- 20
- 60 lb bags
- 26
- Cubic feet
- 11.51 ft³
- Cubic meters
- 0.33 m³
- Weight (wet)
- 1,726 lb
Includes your waste allowance. Bag yields: 40 lb = 0.30 ft³, 60 lb = 0.45 ft³, 80 lb = 0.60 ft³.
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Frequently asked questions
How many bags of concrete for a 4x4 fence post?
For a 10 in hole 2.5 ft deep, plan about 3 bags of 50 lb fast-setting concrete per post (2 bags of 80 lb). An 8 in hole 2 ft deep needs about 1.5 bags of 50 lb.
How deep should fence posts be?
About one third of the above-ground height plus 6 in of gravel — 2.5–3 ft for a 6 ft fence — and below your frost line in cold climates.
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Estimates only. Check quantities with your supplier or contractor before ordering.