Concrete Slab Calculator
Estimate exactly how much concrete is required for your slab, patio, or footing in cubic yards and pre-mix bags. Professional planning for durable construction.
Cubic Yards (yd³)
60lb Bags
80lb Bags
Concept Overview
Concrete volume is a three-dimensional measurement that combines length, width, and thickness. For residential projects like patios and driveways, accuracy is critical to prevent paying for "short-load" delivery fees or running out of pre-mix bags in the middle of a pour.
Standard Thickness
Patios and walkways are typically 4 inches thick. For residential driveways carrying heavy vehicles, a thickness of 5 to 6 inches is recommended.
Ready-Mix vs Bags
Ready-mix is sold by the cubic yard (27 cubic feet). For smaller projects under 1 cubic yard, pre-mix bags are often more cost-effective.
Volume Formula
Cubic Yard Equation
Yards³ = (L' × W' × (D" ÷ 12)) ÷ 27
Always ensure length and width are in feet and depth is converted from inches to feet by dividing by 12.
The 10% Waste Rule
- Order 10% extra for ready-mix spillage
- Account for variations in subgrade depth
- Allow for concrete remaining in the truck drum
- Cheaper than paying a second delivery fee
Bag Yield Estimates
A standard 80lb bag of pre-mix concrete yields 0.6 cubic feet of wet concrete. To fill one cubic yard, you would need 45 bags of 80lb pre-mix.
Common Slab Coverage (4")
Dimensions (ft) Cubic Yards 80lb Bags 10 x 10 1.23 yd³ 56 12 x 12 1.78 yd³ 80 15 x 15 2.78 yd³ 125 20 x 20 4.94 yd³ 223 24 x 24 7.11 yd³ 320 Frequently Asked Questions