Concrete Square Footage Calculator
Calculate concrete area in square feet, then convert to cubic yards based on slab thickness. Concrete is poured by volume but designed by area.
Concrete Area Calculator
From square feet to cubic yards
Concrete is ordered in cubic yards. To convert: (square feet × thickness in feet) ÷ 27. A 200 sq ft slab at 4 inches (0.33 ft) thick needs (200 × 0.33) ÷ 27 = 2.4 cubic yards. Round up to 2.5 yards when ordering.
Standard thicknesses: 4 inches for sidewalks and patios, 5–6 inches for driveways, 6 inches or more for vehicle pads with heavy loads.
Always overorder slightly
Concrete is unforgiving — when the truck leaves, that's what you've got. Always order 5–10% extra to account for grade variations, formwork bulge, and overpour.
Most ready-mix companies have a minimum order (usually 1 yard) and charge a "short load" fee for orders under 3–4 yards. For small slabs, bagged concrete may actually be cheaper.
Square feet vs cubic yards (you'll need both)
Concrete is poured at a thickness, so the calculation needs three dimensions, not two. Concrete is priced and ordered by cubic yards, but slabs are usually planned by square feet.
Conversion formula: cubic yards = (length × width × thickness in inches) ÷ 12 ÷ 27.
Standard slab thicknesses: patio 4 inches, driveway 4-6 inches, garage floor 4-6 inches, sidewalk 4 inches, RV pad 6-8 inches, foundation footings 8-12 inches.
Worked example: 20 × 30 ft patio at 4 inches = (20 × 30 × 4) ÷ 12 ÷ 27 = 7.4 cubic yards. Always order at least 10% extra for irregularity in the subgrade.
Standard ready-mix delivery is in 1-yard increments, minimum 1-3 yards. Below that, use bagged concrete (60 lb bag = 0.45 cu ft; an 80 lb bag = 0.6 cu ft).
Common slab and footprint sizes
Concrete projects typically follow standard dimensions. Knowing these helps with rough budgeting:
Garage floor (2-car): 400 sq ft (20×20). At 4 inches: 4.94 cu yd. At 6 inches: 7.4 cu yd.
Driveway (single-car length): 18 × 10 ft = 180 sq ft. At 4 inches: 2.22 cu yd. At 6 inches: 3.33 cu yd.
Driveway (two-car width, 20 ft length): 20 × 20 = 400 sq ft. At 4 inches: 4.94 cu yd.
Standard patio: 12 × 12 = 144 sq ft. At 4 inches: 1.78 cu yd.
Large entertaining patio: 20 × 30 = 600 sq ft. At 4 inches: 7.4 cu yd.
Sidewalk: 50 linear ft × 4 ft wide = 200 sq ft. At 4 inches: 2.47 cu yd.
Shed pad: 12 × 16 = 192 sq ft. At 4 inches: 2.37 cu yd.
What concrete actually costs
Ready-mix concrete pricing varies by region and additives:
Standard 3,000 PSI concrete: $130-180 per cubic yard (2024 averages, delivered).
4,000 PSI (driveways, structural): $145-200 per cubic yard.
5,000 PSI (commercial, high-load): $170-225 per cubic yard.
Add cost per yard: fiber mesh reinforcement ($8-15/yard), color additive ($35-75/yard), accelerator for cold weather ($15-25/yard), retarder for hot weather ($8-15/yard).
Delivery fees: $50-200 per delivery, often with minimum yard requirements (3-5 yards typical minimum).
Total installed costs (materials + labor + finishing): $4-8 per sq ft for plain concrete, $8-15 for stamped or stained, $15-25 for decorative finishes.
Pro tips
Compact your base
A poorly-compacted gravel base will allow concrete to settle unevenly. Compact in 2-inch lifts before pouring.
Add reinforcement
Wire mesh or rebar is critical for any slab over 100 sq ft. It prevents cracks and extends slab life.
Plan for control joints
Saw-cut control joints every 8–12 ft prevent random cracking. Plan their location before pouring.
Consider weather
Don't pour concrete below 40°F or above 90°F without admixtures. Hot weather requires retarders; cold needs accelerators.