Concrete Calculator
Concrete Slab
Calculate concrete needed for a rectangular slab or patio
Concrete Column / Post Hole
Calculate concrete for round columns or post holes
Formula
Volume = L × W × D (in feet) | Cubic Yards = Volume / 27 | Bags = Volume / 0.6
Frequently Asked Questions
How do I calculate concrete for a slab?
Multiply length × width × thickness (in feet). Divide by 27 to get cubic yards. Add 10% for waste. Example: 20ft × 10ft × 4in thick = 200 × 0.333 = 66.7 cu ft = 2.47 cu yd + 10% = 2.72 cu yd.
How many bags of concrete do I need?
One 80-lb bag covers about 0.6 cubic feet. For a 4' × 4' × 4" slab: 4 × 4 × 0.333 = 5.33 cu ft → 9 bags. For large projects (over 1 cubic yard), order ready-mix delivery instead.
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