Calculate exactly how much concrete, rebar, and mesh you need for any slab project. Estimates cubic yards, reinforcement materials, and total material costs.
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576 sq ft at 4" thick (incl. 10% waste)
| Slab Area | 576 sq ft |
|---|---|
| Concrete (net) | 7.1 cu yd |
| Concrete (with waste) | 7.8 cu yd |
| Rebar Pieces | 34 |
| Rebar Linear Feet | 816 |
| Concrete Cost | $1,212.44 |
| Rebar Cost | $612.00 |
| Wire Mesh Cost | $326.40 |
| Vapor Barrier Cost | $69.70 |
| Total Material Cost | $2,220.54 |
| Cost per Sq Ft | $3.86 |
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Concrete slab construction involves several cost components that vary significantly by region, project size, and specifications. In 2026, the average cost of a basic concrete slab ranges from $6 to $10 per square foot for a standard 4-inch residential slab with basic finishing. This includes ready-mix concrete delivery, rebar or wire mesh reinforcement, vapor barrier, forming, placement, and basic broom or trowel finishing.
The largest single cost is the concrete itself. Ready-mix concrete averages $140 to $170 per cubic yard delivered in most US markets. A 20x20-foot slab at 4 inches thick requires approximately 5 cubic yards of concrete, costing $700 to $850 for material alone. However, many concrete suppliers charge short-load fees for orders under 5 to 7 yards, adding $50 to $100 per cubic yard to the base price.
Choosing the right slab thickness is critical for both structural performance and cost control. Residential patios and walkways perform well at 4 inches. Garage floors should be a minimum of 5 inches, with 6 inches preferred for heavy vehicles or workshop use. Driveways need 5 to 6 inches for passenger vehicles and 6 to 8 inches if trucks or RVs will be parked regularly. Each additional inch of thickness adds roughly 25 percent more concrete. For a 20x20 slab, going from 4 to 6 inches adds about 2.5 cubic yards and $375 to $425 in concrete cost alone.
Proper reinforcement prevents cracking and extends slab life by decades. The two primary options are welded wire mesh and rebar. Wire mesh (6x6 W1.4/W1.4) costs approximately $85 per 150-square-foot roll and works well for lightly loaded 4-inch slabs. Rebar provides superior reinforcement and is required for thicker slabs and structural applications. Number 4 rebar (half-inch diameter) at 18-inch spacing on center is the most common residential specification, costing approximately $0.75 per linear foot. For a 24x24-foot slab, you need roughly 64 bars totaling about 700 linear feet, costing $525 in rebar alone.
The single most important factor in slab longevity is proper subgrade preparation. The subgrade should be compacted to 95 percent standard Proctor density. Most contractors use 4 to 6 inches of compacted gravel base (Class 5 aggregate) over undisturbed soil. This base layer costs $1.50 to $2.50 per square foot installed. Poor subgrade preparation leads to differential settlement, which causes cracking that no amount of reinforcement can prevent. In areas with expansive clay soils, a 6 to 8 inch gravel base with proper drainage is essential.
Basic broom finish is included in standard slab pricing. Smooth trowel finish adds $0.50 to $1.00 per square foot. Exposed aggregate finish costs $2 to $4 per square foot extra and creates an attractive, slip-resistant surface. Stamped concrete adds $4 to $10 per square foot but can mimic stone, brick, or tile at a fraction of the cost. Colored concrete using integral color additives adds $1 to $2 per square foot. Acid staining existing concrete costs $2 to $4 per square foot and creates unique, variegated color patterns.
Concrete costs vary significantly by region. The Northeast and West Coast markets are typically 15 to 25 percent higher than national averages, with concrete at $160 to $190 per cubic yard. Midwest and Southern markets tend to be at or below average, ranging from $130 to $155 per cubic yard. Urban areas generally cost more due to higher labor rates, traffic management requirements, and limited access for concrete trucks. Rural areas may see higher delivery costs due to distance from batch plants.
Calculating concrete volume starts with a simple formula: Length (feet) multiplied by Width (feet) multiplied by Thickness (feet), then divided by 27 to convert cubic feet to cubic yards. Since thickness is usually specified in inches, divide the inch measurement by 12 first. For a 20x20-foot slab at 4 inches thick, the calculation is 20 times 20 times 0.333 (4 divided by 12), which equals 133.2 cubic feet, then divide by 27 to get 4.93 cubic yards.
For irregularly shaped slabs, break the area into rectangles and calculate each section separately. For circular slabs like fire pit pads, use the formula pi times radius squared times thickness divided by 27. A 10-foot diameter circular pad at 4 inches thick requires pi times 5 squared times 0.333 divided by 27, which equals 0.97 cubic yards.
Never order the exact calculated amount of concrete. Real-world conditions always require more material than the theoretical calculation suggests. Uneven subgrade means some areas will be slightly thicker than planned. Concrete inevitably spills during placement. Forms may bow slightly, increasing volume. The standard recommendation is 5 to 10 percent extra for simple rectangular slabs and 10 to 15 percent for complex shapes or sloped sites.
Running short on concrete is far more expensive than ordering slightly too much. If a ready-mix truck leaves and you need more, you will pay a full short-load delivery fee for a fraction of a yard. Some contractors have been burned by this and routinely order 15 percent extra for any project, preferring to pour the excess into small pad areas or simply waste it rather than risk a cold joint from a second delivery.
One cubic yard of concrete covers the following areas at various thicknesses: at 3 inches thick, one yard covers 108 square feet; at 4 inches, 81 square feet; at 5 inches, 64.8 square feet; at 6 inches, 54 square feet; and at 8 inches, 40.5 square feet. These figures are useful for quick mental estimates. A two-car garage at 20x24 feet (480 square feet) at 6 inches thick needs approximately 8.9 cubic yards, or about 10 yards with waste factor.
For rebar reinforcement, count the number of bars needed in each direction. At 18-inch (1.5-foot) spacing on a 24-foot-wide slab, you need 24 divided by 1.5 plus 1 equals 17 bars running the length. Repeat for the perpendicular direction. Multiply bar count by bar length to get total linear footage. Add 10 percent for overlap at splices, which require a minimum 24-inch overlap for number 4 rebar. For wire mesh, calculate the slab area and add 10 percent for overlap between sheets.
Schedule your pour for a weekday, as Saturday deliveries typically carry a $50 to $150 surcharge. Combine small pours into one larger delivery to avoid short-load fees. Many suppliers offer a price break at 5 or 10 yards. If your project requires 4.5 yards, consider slightly increasing the slab thickness or adding a small adjacent pad to reach the 5-yard threshold. Coordinate with neighbors who may also need concrete to share a delivery and split the delivery fee.
Standard residential slabs are 4 inches thick. Garage floors and driveways should be 5 to 6 inches. Heavy-duty applications like commercial floors or areas supporting heavy equipment need 6 to 8 inches. Every additional inch of thickness adds roughly 25% more concrete per square foot.
A 20x20-foot slab at 4 inches thick requires approximately 4.94 cubic yards. At 6 inches thick, you need about 7.41 cubic yards. Always order 5 to 10 percent extra to account for spillage, uneven subgrade, and over-excavation.
In 2026, a basic concrete slab costs $6 to $10 per square foot for materials and labor. Stamped or decorative concrete runs $12 to $20 per square foot. Material costs alone (concrete, rebar, vapor barrier) typically run $3 to $5 per square foot.
Rebar is recommended for slabs thicker than 4 inches, driveways, and any slab that will bear heavy loads. For a standard 4-inch patio slab on stable ground, welded wire mesh (6x6 W1.4/W1.4) may suffice. Most building codes require rebar for structural slabs.
Concrete reaches about 70 percent strength in 7 days and full design strength (typically 4,000 PSI) in 28 days. You can walk on it after 24 to 48 hours and drive on it after 7 days. Keep it moist for the first 7 days for optimal curing.
For most residential slabs, a standard 4,000 PSI mix is ideal. In cold climates, specify air-entrained concrete (6 percent air) to resist freeze-thaw cycles. For driveways and garage floors, consider 4,500 PSI mix for extra durability.
Yes, a 10-mil polyethylene vapor barrier is recommended under any interior slab or slab that will receive flooring. It prevents moisture from wicking up through the concrete, which can damage flooring and promote mold growth. Overlap seams by 6 inches.
In 2026, ready-mix concrete costs $140 to $170 per cubic yard delivered, depending on your region and mix design. Short-load fees of $50 to $100 per yard apply for orders under 5 to 7 cubic yards. Saturday delivery and special mixes cost extra.
Volume = Length x Width x (Thickness / 12) / 27
Result in cubic yards, with waste factor applied
Rebar count = bars in each direction at specified spacing
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