Garage Floor Concrete Guide
Garage floors take more abuse than any other concrete slab in your home. Vehicles, tools, salt, oil, freeze-thaw cycles — a garage floor needs to be thicker, stronger, and better reinforced than a patio or walkway. The standard is 4 inches minimum, but 6 inches with rebar is recommended for any garage that stores vehicles heavier than a passenger car.
2-car garage: 20 × 24 ft (480 sq ft) = 5.93 cu yd at 4 in
3-car garage: 30 × 24 ft (720 sq ft) = 8.89 cu yd at 4 in
At 6 inches: multiply by 1.5
Reinforcement
Garage floors should always be reinforced. At minimum, use 6×6 welded wire mesh (WWM). For heavy vehicles or equipment: #4 rebar at 12 inches on center in both directions. The Rebar Calculator can estimate the steel. Place reinforcement at mid-depth in the slab — chairs or dobies hold it off the subgrade.
The floor should slope 1/8 to 1/4 inch per foot toward the garage door for drainage. A 24-foot deep garage needs 3–6 inches of total fall from back wall to door opening.