Free Concrete Calculator — Cubic Yards for Slabs & Footings | NovaCalculator
Calculate how much concrete you need for slabs, footings, columns, and steps in cubic yards or cubic feet. Free concrete volume calculator for any project.
Formula
Volume = Length × Width × Depth (for slabs)
Calculate volume in cubic feet, then divide by 27 to get cubic yards. For columns, use π × r² × height. Add 10% for waste.
Worked Examples
Example 1: Driveway Slab Calculation
Problem:Calculate concrete needed for a 20-foot long, 10-foot wide driveway with 5-inch thickness.
Solution:Convert thickness to feet: 5 inches ÷ 12 = 0.417 feet\n\nVolume = Length × Width × Depth\nVolume = 20 × 10 × 0.417 = 83.4 cubic feet\n\nConvert to cubic yards:\n83.4 ÷ 27 = 3.09 cubic yards\n\nAdd 10% for waste: 3.09 × 1.10 = 3.4 cubic yards
Result:Order 3.5 cubic yards of ready-mix concrete
Example 2: Fence Post Footings
Problem:Calculate concrete for 10 fence post holes, each 10 inches diameter and 24 inches deep.
Solution:Radius = 10 inches ÷ 2 = 5 inches = 0.417 feet\nHeight = 24 inches = 2 feet\n\nVolume per hole = π × r² × h\nVolume = 3.14 × 0.417² × 2 = 1.09 cubic feet\n\nTotal for 10 holes = 1.09 × 10 = 10.9 cubic feet\n\n80-lb bags needed = 10.9 ÷ 0.022 = 496 ≈ 50 bags
Result:Need approximately 50 80-lb bags for 10 post holes
Example 3: Patio with Steps
Problem:Calculate concrete for a 12×15 ft patio (4 inches thick) plus 2 steps (4 ft wide × 1 ft deep × 7 inches high each).
Solution:Patio:\n12 × 15 × (4/12) = 60 cubic feet\n\nSteps (each):\n4 × 1 × (7/12) = 2.33 cubic feet\nTwo steps = 4.67 cubic feet\n\nTotal = 60 + 4.67 = 64.67 cubic feet\n64.67 ÷ 27 = 2.40 cubic yards\n\nWith 10% extra: 2.64 cubic yards
Result:Order 3 cubic yards for patio and steps
Frequently Asked Questions
How much concrete do I need for a 10x10 slab?
For a 10x10 foot slab at standard 4-inch thickness: Volume = 10 × 10 × (4/12) = 33.33 cubic feet = 1.23 cubic yards. Order about 1.5 yards to account for waste and spillage. For bags, you'd need approximately 45 80-lb bags, 60 60-lb bags, or 91 40-lb bags.
How do I calculate concrete for a circular column?
Use the formula: Volume = π × r² × height, where r is the radius (diameter/2). For a 12-inch diameter, 3-foot tall column: radius = 6 inches = 0.5 feet, Volume = 3.14 × 0.5² × 3 = 2.36 cubic feet. For multiple columns, multiply by quantity. Always round up and add 10% for waste.
What's the difference between ready-mix and bagged concrete?
Ready-mix is delivered by truck, pre-mixed to specification. Best for large projects (over 1 cubic yard). Bagged concrete (40-80 lb bags) is mixed on-site with water. Better for small projects, repairs, and DIY. Ready-mix is more consistent, saves labor, but has minimum orders (~1 yard) and delivery fees.
How thick should my concrete slab be?
Thickness depends on use: Sidewalks/patios: 4 inches minimum. Driveways (cars): 4-5 inches. Driveways (heavy vehicles): 5-6 inches. Garage floors: 4-6 inches. Foundation slabs: 4-8 inches with reinforcement. Always check local building codes - they may require specific thicknesses and reinforcement.