Concrete Slab Calculator
Estimate the concrete volume for any slab, patio, or floor in cubic yards, cubic feet, and cubic meters. Enter your length, width, and thickness; the calculator handles the unit conversions and shows the exact ready-mix order quantity. Built for contractors pouring footings to driveways and DIYers planning a single patio.
Slab dimensions diagram
How the Formula Works
Convert thickness to feet
Thickness (ft) = Thickness (in) ÷ 12 Thickness is entered in inches but all three dimensions must share the same unit before multiplying
Calculate volume in cubic feet
Volume (ft³) = Length (ft) × Width (ft) × Thickness (ft) Convert to cubic yards
Volume (yd³) = Volume (ft³) ÷ 27 There are 27 cubic feet in one cubic yard — the standard US ready-mix order unit
Convert to cubic meters (optional)
Volume (m³) = Volume (ft³) × 0.0283168 Frequently Asked Questions
For most residential applications, 4 inches (100 mm) is standard. Driveways typically need 4–6 inches, garage floors 4–6 inches, and structural slabs can be 6–8 inches or more depending on load requirements.
An 80 lb bag of concrete mix yields about 0.60 cubic feet. Divide your total cubic feet by 0.60 to get the bag count. For larger pours, ordering ready-mix concrete by the cubic yard is more economical than bags.
A cubic yard is 3 ft × 3 ft × 3 ft = 27 cubic feet. Ready-mix concrete in the US is ordered and priced by the cubic yard. One cubic yard weighs approximately 4,000 lbs (1,814 kg).
Yes — most contractors recommend ordering 5–10% extra to account for spillage, uneven subgrade, and formwork variation. Running short mid-pour is far more costly than a little left over.
Rebar or welded wire mesh is strongly recommended for slabs larger than 10 × 10 ft, driveways, and any slab subject to heavy loads. Reinforcement doesn't change concrete volume but significantly improves crack resistance.
Break the area into rectangles, run this calculator for each section, and add the volumes. For example, an L-shaped slab can be split into two rectangles.
References
- American Concrete Institute ACI 318 – Building Code Requirements for Structural Concrete
- Portland Cement Association (PCA) Design and Control of Concrete Mixtures
- International Residential Code IRC R506 – Concrete Floors on Ground