Free concrete slab calculator for driveways, patios, garage floors, and sidewalks. Get cubic yards, bag count, and material cost in seconds, with waste factor included.
Choosing the right slab thickness is one of the most important decisions in any concrete project. Too thin and the slab will crack under load. Too thick and you waste money on unnecessary material. Here are the standard thicknesses recommended by the American Concrete Institute (ACI) and common industry practice:
Standard for pedestrian foot traffic. Use 3000 PSI concrete with welded wire mesh or fiber reinforcement. Suitable for residential walkways, garden paths, and light-duty applications.
A 4-inch patio slab handles outdoor furniture, grills, and foot traffic with ease. Consider going to 6 inches if you plan to install a hot tub or other heavy equipment on the patio.
Residential driveways for passenger vehicles need at least 4 inches, but 5 to 6 inches is recommended for longevity. If heavy trucks or RVs will use the driveway, go with 6 inches minimum.
Garage slabs need extra thickness to support vehicles, heavy equipment, and storage. A 6-inch slab with rebar on 18-inch centers is standard. Go to 8 inches for workshops or commercial use.
Let's walk through a real-world example. You want to pour a new driveway that measures 20 feet long by 20 feet wide at a thickness of 6 inches (0.5 feet). Here is how the math works:
Volume = Length x Width x Thickness
Volume = 20 ft x 20 ft x 0.5 ft
Volume = 200 cubic feet
Convert to cubic yards: 200 / 27 = 7.41 cubic yards
Add 10% for waste: 7.41 x 1.10 = 8.15 cubic yards
You would order 8.25 cubic yards from your ready-mix supplier (most deliver in quarter-yard increments). At $110 to $150 per cubic yard for standard 3,000 PSI concrete, the concrete for this driveway would cost roughly $908 to $1,238 before any delivery or short-load fees. The calculator above does this math, including bag counts if you prefer to mix your own.
Reinforcement prevents cracks from spreading and holds the slab together if the ground shifts beneath it. The two most common options for slab reinforcement are welded wire mesh and rebar. Here is when to use each:
For the best of both worlds, many contractors use fiber-reinforced concrete (with polypropylene or steel fibers mixed into the batch) combined with wire mesh. This helps control plastic shrinkage cracking in the first 24 hours while the mesh handles structural loads long-term.
A concrete slab is only as good as the ground beneath it. Poor sub-base preparation is the number one cause of cracking, settling, and premature failure. Before you pour a single yard of concrete, invest the time to get your base right:
Prices checked October 31, 2026. These are national ranges from the cost guides below; prices vary by region, so get a local quote before you order.
The required thickness depends on the application. Sidewalks and patios typically need 4 inches. Residential driveways should be 4 to 6 inches thick. Garage floors and areas supporting heavy loads need 6 to 8 inches. Always check your local building codes for specific requirements.
A 10x10 foot slab at 4 inches thick requires approximately 1.23 cubic yards of concrete. That equals roughly 56 bags of 80-pound premixed concrete or 75 bags of 60-pound mix before any waste allowance. For a project this size, ordering ready-mix concrete by the yard is usually more cost-effective.
For most residential slabs like patios and sidewalks, welded wire mesh or fiber reinforcement is sufficient. Driveways benefit from #3 or #4 rebar on 18-inch centers due to vehicle loads. Garage floors and any slab over 5 inches thick should include rebar for structural integrity.
Concrete gains strength gradually. You can walk on it after 24 to 48 hours. Light vehicle traffic is safe after 7 days. Full design strength (typically 3000 to 4000 PSI) is reached at 28 days. Keep the slab moist for the first 7 days for the best results.
A basic 4-inch concrete slab costs about $6 to $8 per square foot installed. A contractor's price normally includes site preparation, forms, concrete, finishing and basic reinforcement. Stamped concrete runs about $8 to $19 per square foot installed. If you place and finish it yourself with ready-mix, the concrete for a 4-inch slab costs about $1.36 to $1.85 per square foot (one cubic yard covers 81 square feet at 4 inches). Sources and dates are listed below.
