Concrete Slab, Column & Bag Calculator
Estimate structural concrete requirements instantly. Calculate cubic yards, weight in tons, and retail bag counts for slabs, post holes, and columns with interactive rebar projections.
Project Parameters
💰 Local Ready-Mix & Bag Costs
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1.36yd³
Equivalent to 36.7 cu ft or 1.04 m³
3D Structural Project Visualizer
📦 Dry Mix Bag Pallet Stacker
(62 bags)💵 Purchase Economics Forecast
Concrete Slab & Column Volume Estimation Guide
How is concrete volume calculated?
To find the volume for a rectangular concrete slab, multiply Length (ft) by Width (ft) by Thickness (converted to feet: inches / 12) to get cubic feet. Divide by 27 to convert cubic feet to cubic yards ($yd^3$). For cylindrical columns (like post holes or pier footings), multiply $\pi$ by radius squared (in feet) by depth (in feet), then multiply by quantity.
How many bags of concrete do I need?
Pre-mixed dry concrete is sold in standard bags. Each bag yield is fixed: an 80lb bag yields 0.60 cubic feet, a 60lb bag yields 0.45 cubic feet, and a 40lb bag yields 0.30 cubic feet. Therefore, 1 cubic yard ($27\textft^3$) requires exactly 45 bags (80lb), 60 bags (60lb), or 90 bags (40lb). Always add a 5-10% waste buffer to account for uneven grade!
Is it cheaper to buy bulk or bagged concrete?
For small projects under 1 cubic yard (such as post holes, small footers, or garden borders), buying retail bags is more economical and easier to transport. For larger projects over 1-2 cubic yards, ordering a delivery from a ready-mix truck (charged per cubic yard, typically with a minimum load fee) becomes significantly cheaper and saves hours of intense manual labor.