SPECIFICATION: 2-Car Garage Floor, Heavy Equipment Parking, RV Pad

20×20 Garage Concrete Slab Calculator (Vehicle Rated)

A 20×20 slab designed for vehicle traffic must be poured at least 5 to 6 inches thick using 4,000 PSI concrete. At 6 inches, this 400 sq ft slab consumes 7.41 net cubic yards (8.15 cubic yards with 10% waste buffer). This requires a full commercial ready-mix mixer truck delivery.

SLAB DIMENSIONS400 SQ FT
THICKNESS (INCHES)6" Depth
+10%
DIY Retail Bag Weight:
Live Structural Cross-Section
20' × 20' Slab (6" Depth)
Structural cross-section of 20' x 20' concrete slab6" CONCRETE6" #57 STONE#4 REBAR @ 12" O.C.10 MIL VAPOR BARRIERCOMPACTED SUBGRADESPAN: 20 FT × 20 FT
Net Volume:7.41 cu yds
Order (+Waste):8.15 cu yds
Base Prep:6" Crushed Base
Reinforcement:#4 @ 12" O.C.
Yield Comparison (20' × 20')
DIY RETAIL STORE PICKUP
367 Bags
80 lb bags (~9 full pallets)
Dry Weight:29,360 lbs
Est. Bag Cost:$2,386
COMMERCIAL READY-MIX
8.15 cu yds
1 mixer truck (4000 PSI)
Delivery Scale:Recommended for Ready-Mix
Est. Ready-Mix:$1,263

Frequently Asked Questions: 20×20 Garage Concrete Slab Calculator (Vehicle Rated)

How many cubic yards of concrete for a 20x20 slab at 6 inches?

You need 8.15 cubic yards of concrete (7.41 net yards + 10% waste tolerance). A standard mixer truck holds 9-10 yards, meaning a single full truckload easily covers the pour.

Can you use bagged concrete for a 20x20 garage floor?

No. An 8.15-yard pour requires 367 bags of 80 lb concrete (nearly 9 full pallets weighing almost 30,000 lbs). Attempting to hand-mix this will ruin the structural integrity of the floor.

What rebar grid is specified for a vehicle garage slab?

#4 rebar spaced on a tight 12" on-center grid tied with wire at intersections and set on 3" chairs is standard for passenger cars, SUVs, and heavy light-duty trucks.