How Much Concrete for a 20x20 Slab?
Quick Answer
For a standard 4-inch thick 20x20 foot slab, you will need approximately 4.94 cubic yards of concrete. We recommend ordering 5.5 cubic yards to account for a 10% waste margin.
Detailed Explanation
Calculating the concrete needed for a 20x20 slab is straightforward once you know the formula. Concrete is ordered by volume in cubic yards, so we must convert all our measurements into feet, find the cubic feet, and then convert to cubic yards.
Step-by-Step Math Breakdown
1. Convert thickness to feet: 4 inches ÷ 12 = 0.333 feet
2. Calculate square footage: 20 ft × 20 ft = 400 sq ft
3. Calculate cubic feet: 400 sq ft × 0.333 ft = 133.33 cubic feet
4. Convert to cubic yards: 133.33 ÷ 27 = 4.94 cubic yards
2. Calculate square footage: 20 ft × 20 ft = 400 sq ft
3. Calculate cubic feet: 400 sq ft × 0.333 ft = 133.33 cubic feet
4. Convert to cubic yards: 133.33 ÷ 27 = 4.94 cubic yards
Materials Note
Standard concrete weighs about 150 lbs per cubic foot. A 20x20 slab at 4 inches thick will weigh approximately 20,000 lbs (10 tons). Because of this massive weight, you will definitely want to order ready-mix concrete delivered by a truck rather than mixing bags by hand.