How Much Concrete for a 20x20 Slab (4" Deep)?
Material takeoff and yardage calculator for a 20 ft × 20 ft concrete slab poured at 4 inches depth. Includes 10% safety margin for formwork deflection and subgrade settling.
Excavation, Base & Reinforcement Specifications
Custom Volume Engine#3 Rebar (3/8") or 6x6 W1.4/W1.4 welded wire mesh placed on 2" chairs
Frequently Asked Concrete Questions
How many yards of concrete do I need for a 20x20 slab at 4 inches thick?
For a 20ft by 20ft slab poured at 4 inches deep, the exact net volume is 4.94 cubic yards (133.3 cubic feet). Always order with a 10% safety margin for subbase settling and form deflection, bringing your total order to 5.43 cubic yards.
How many bags of concrete does it take to pour a 20x20 slab?
If mixing by hand, you will need approximately 245 bags of 80lb concrete (or 326 bags of 60lb concrete) including 10% waste buffer. Because this exceeds 2.5 cubic yards, ordering ready-mix truck delivery is strongly recommended over mixing bags by hand.
Is 4 inches thick enough for a standard 2-car garage slab?
Yes. A 4-inch slab is the residential building code standard for pedestrian patios, walkways, storage sheds, and standard passenger cars (under 6,000 lbs).
What gravel base and rebar reinforcement is needed?
Excavate 8 to 10 inches total. Install 5.68 cubic yards of crushed gravel (compacted to 4 inches). Support your #3 Rebar (3/8") or 6x6 W1.4/W1.4 welded wire mesh placed on 2" chairs so it sits in the middle third of the slab pour.