Plan your concrete slab pour with precision. This calculator estimates concrete volume (cubic yards and cubic feet), bag count (80 lb and 60 lb), ready-mix truck requirements, rebar quantity, form lumber, and a complete cost breakdown including materials and labor. Ideal for patios, driveways, shed foundations, and garage slabs.
4" for patios, 5–6" for driveways.
10% recommended. Accounts for spillage, uneven ground, and over-excavation.
Center-to-center grid spacing.
US average: $150/yd³ delivered.
#4 (½") rebar, 20 ft length.
Typical concrete crew rate.
📊 Concrete Slab Estimate
Slab Area—
Volume — Cubic Feet—
Volume — Cubic Yards—
Volume with Waste Factor—
80 lb Bags Needed—
60 lb Bags Needed—
Ready-Mix Trucks (10 yd³ each)—
Rebar Sticks Needed (#4, 20 ft)—
Form Lumber (linear ft)—
💰 Concrete Cost—
💰 Rebar Cost—
💰 Form Lumber Cost—
💰 Labor Cost (est.)—
💰 TOTAL ESTIMATED COST—
Estimates based on national averages. Actual costs vary by location. Always get multiple quotes from local contractors.
How to Use the Concrete Slab Calculator
Enter your slab's length, width, and thickness in feet and inches. The calculator instantly computes the volume in both cubic feet and cubic yards using the formula: Volume = Length × Width × (Thickness ÷ 12). A 10% waste factor is applied by default to account for spillage, uneven ground, and minor over-excavation — you can adjust this for your project.
The bag count tells you exactly how many 80 lb or 60 lb bags to purchase if you're mixing by hand. One 80 lb bag yields approximately 0.6 cubic feet of mixed concrete. For larger pours, the ready-mix truck estimate tells you how many 10-cubic-yard trucks you'll need. Most suppliers have a minimum 1-yard order and charge short-load fees for orders under 5 yards.
The rebar estimate calculates the number of 20-foot #4 (½-inch) rebar sticks needed for a grid at your selected spacing. The form lumber calculation gives you the total linear feet of 2× lumber needed to build the perimeter form. The cost breakdown separates concrete, rebar, form lumber, and labor so you can see where your budget is going.
Concrete Slab Pouring Tips
Prep your sub-base. Excavate to the proper depth, compact the soil, and add 4–6 inches of compacted gravel. A solid sub-base prevents cracking and frost heave.
Use vapor barrier for interior slabs. Place 6-mil polyethylene sheeting under garage and basement slabs to prevent moisture migration through the concrete.
Order the right slump. A 4-inch slump is standard for most slabs. Too wet and you lose strength; too dry and it's hard to work and finish.
Plan your control joints. Cut control joints at 2–3 times the slab thickness in feet (e.g., every 8–12 ft for a 4-inch slab). This controls where the concrete cracks.
Cure properly. Concrete reaches its design strength after 28 days of curing. Keep the slab moist for at least 7 days — spray with water or use a curing compound.
A 20 ft × 20 ft slab at 4 inches thick requires approximately 4.94 cubic yards of concrete (before waste factor). With a 10% waste factor, plan for about 5.44 cubic yards. At 6 inches thick (driveway), you'd need about 7.41 cubic yards before waste. Our calculator does this math instantly — just enter your dimensions above.
Use ready-mix delivery for any slab over 1 cubic yard (about 45 bags). It's cheaper per yard, consistent in quality, and saves hours of mixing. Bagged concrete is practical for small pads, repairs, or projects under 20 bags. A 10×10 patio at 4 inches is about 1.23 yards — that's 56 bags of 80 lb mix. Most DIYers hire a ready-mix truck for anything beyond a small shed slab.
Rebar quantity depends on your grid spacing. For a standard 18" OC grid, you need approximately one #4 rebar stick (20 ft) for every 30 square feet of slab area. A 20×12 slab (240 sq ft) needs about 8 sticks for the length direction and 14 sticks for the width direction — about 22 total 20-ft sticks. Our calculator computes this based on your chosen spacing. Wire mesh (6×6 W1.4/W1.4) is an alternative for lighter-duty slabs.
A basic 4-inch concrete slab typically costs $5–$8 per square foot for materials and labor. Concrete itself is about $1.85/sq ft at 4" thick ($150/yd³). Rebar adds $0.50–$1.00/sq ft. Form lumber adds $0.25–$0.50/sq ft. Labor for pouring and finishing is typically $2–$4/sq ft. Total cost for a professional pour ranges from $5–$10/sq ft depending on thickness, finish (broom, stamped, exposed aggregate), and regional labor rates.
Standard slab thickness depends on use: 4 inches for patios, walkways, and shed floors; 5–6 inches for residential driveways (standard vehicles); 6+ inches for garage floors, RV pads, or areas with heavy vehicles. Always check local building codes — many municipalities require a minimum of 4 inches with reinforcement. In freeze-thaw climates, the slab edges should be thickened to 12 inches (a "thickened edge" or "turn-down" slab) to resist frost heave.