How Much Concrete for a 20x20 Slab (6" Deep)?
Material takeoff and yardage calculator for a 20 ft × 20 ft concrete slab poured at 6 inches depth. Includes 10% safety margin for formwork deflection and subgrade settling.
Excavation, Base & Reinforcement Specifications
Custom Volume Engine#4 Rebar (1/2") on 16" to 18" grid, elevated on 3" chairs with perimeter thickened edge
Frequently Asked Concrete Questions
How many yards of concrete do I need for a 20x20 slab at 6 inches thick?
For a 20ft by 20ft slab poured at 6 inches deep, the exact net volume is 7.41 cubic yards (200.0 cubic feet). Always order with a 10% safety margin for subbase settling and form deflection, bringing your total order to 8.15 cubic yards.
How many bags of concrete does it take to pour a 20x20 slab?
If mixing by hand, you will need approximately 367 bags of 80lb concrete (or 489 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 6 inches thick enough for a standard 2-car garage slab?
A 6-inch slab is engineered for heavy vehicular traffic, full-size pickup trucks, heavy equipment, RV pads, and automotive lifts (requiring minimum 4.5" to 6" anchor embedment per ACI 318).
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 #4 Rebar (1/2") on 16" to 18" grid, elevated on 3" chairs with perimeter thickened edge so it sits in the middle third of the slab pour.