Free Online Tool
Concrete Calculator — Estimate Volume & Materials
Calculate the exact amount of concrete needed for slabs, footings, and columns. Supports multiple shapes and bag sizes.
3
Slab Shapes
3
Bag Sizes
2
Systems
100%
Free
Enter Project Details
Your Results
Ready to Calculate
Enter your roof dimensions and click Calculate to see material estimates.
📏 Enter length & width📐 Select roof type⚡ Click Calculate
Concrete Volume Formula
Volume = Area × Thickness. For a rectangle: V = L × W × T. For a circle: V = π × (D/2)² × T. For a triangle: V = (B × H / 2) × T.
Concrete Slab Example
Inputs
length20
width12
thickness4
Calculation Steps
1
Area (sq ft)
20 × 12 = 240 sq ft
2
Thickness (ft)
4 ÷ 12 = 0.333 ft
3
Volume (cu ft)
240 × 0.333 = 80 cu ft
4
Volume (cu yd)
80 ÷ 27 = 2.96 cu yd
Final Answer
You need approximately 3 cubic yards of concrete (5.3 tons). Order 1 truck.
Frequently Asked Questions
Measure the length and width of the slab in feet, multiply to get area, then multiply by thickness (in feet) to get cubic feet. Divide by 27 to get cubic yards.
An 80 lb bag yields about 0.6 cu ft, a 60 lb bag yields 0.45 cu ft, and a 40 lb bag yields 0.3 cu ft. Divide your total cubic feet by the bag yield.
Standard ready-mix concrete trucks carry 10 cubic yards. We recommend ordering 1 truck for projects under 10 cu yd.
Patios and walkways: 4 inches. Driveways: 5-6 inches. Heavy vehicle areas: 6-8 inches. Always check local building codes.
Ready-mix concrete costs $100-200 per cubic yard on average. The price varies by region, strength specification, and additives.