How Much Concrete Do I Need? Slab and Footing Calculation Guide

The Fundamental Concrete Volume Formula

Ordering too little concrete leaves a cold joint in your pour, while ordering too much wastes money. Ready-mix concrete suppliers measure volume in cubic yards.

Cubic Yards = [Length (ft) × Width (ft) × Depth (ft)] / 27

Step-by-Step Slab Example

For a 10 ft by 12 ft patio poured 4 inches thick:

• Convert thickness to feet: 4 inches / 12 = 0.333 ft
• Cubic feet: 10 × 12 × 0.333 = 40 cubic feet
• Convert to cubic yards: 40 / 27 = 1.48 cubic yards
• Add 10% for spillage and sub-base unevenness: 1.48 × 1.10 = 1.63 cubic yards

How Many Bags of Concrete Do You Need?

• One 60-pound bag yields approximately 0.45 cubic feet (about 60 bags per cubic yard).
• One 80-pound bag yields approximately 0.60 cubic feet (about 45 bags per cubic yard).

Calculate exact yardage and bag counts for slabs, footings, and cylindrical post holes with our free Concrete Calculator.