Concrete for a 30 × 40 slab
Short answer
A 30 × 40 ft slab at 4" thick needs about 14.81 cubic yards of concrete — roughly 734 80-lb or 978 60-lb pre-mix bags (including 10% waste).
Concrete
14.81 yd³
80-lb bags
734
60-lb bags
978
40-lb bags
1467
30 × 40 slab at 4" thick
A 30 × 40 ft slab is 1200 square feet. At the standard 4-inch thickness that works out to 400 cubic feet, or 14.81 cubic yards including a 10% waste allowance. For a driveway or anything bearing vehicle loads, step up to 5–6 inches.
Different size or thickness?
Open the concrete calculatorOther slab sizes
Frequently asked questions
How much concrete for a 30 × 40 slab?
A 30 × 40 ft slab at 4" thick needs about 14.81 cubic yards (400 cubic feet), including a 10% waste allowance.
How many bags of concrete for a 30 × 40 slab?
About 734 80-lb bags, 978 60-lb bags, or 1467 40-lb bags. Above roughly 1 cubic yard it is usually cheaper to order ready-mix than to buy bags.
Is a 4-inch slab thick enough?
Four inches is standard for patios, walkways, and shed floors. Go to 5–6 inches for driveways or anything carrying vehicle loads. Change the thickness in the calculator to see the new amount.