Concrete Slab Cost Calculator

How Does the Concrete Volume Formula Work?

Concrete volume is calculated in cubic yards because ready-mix is ordered and priced by the cubic yard. The formula converts your slab dimensions from inches and feet into cubic yards using a single divisor.

What is the cubic yard formula for a concrete slab?

Multiply length in feet by width in feet by thickness in feet, then divide by 27. There are 27 cubic feet in one cubic yard, which is where the divisor comes from.

Worked example: a 20-foot by 12-foot patio poured at 4 inches thick. Convert 4 inches to feet first: 4 divided by 12 equals 0.333 feet. Then: 20 × 12 × 0.333 = 79.9 cubic feet. Divide by 27: 79.9 ÷ 27 = 2.96 cubic yards before waste allowance. Round to 3.0 cubic yards as the base figure.

How Much Extra Concrete Should You Order?

Order 10% above the calculated volume on every pour. That allowance covers three sources of loss that are present on nearly every job: spillage at the chute, slight variations in subgrade depth that add volume in low spots, and over-excavation at slab edges where forms sit slightly outside the nominal dimension.

What happens if the concrete runs short mid-pour?

A short pour forces a cold joint, a visible seam where fresh concrete meets a partially set batch. A cold joint is a structural weakness and a cosmetic defect. Calling for an emergency half-load to finish a short pour also triggers a short-load fee of $75 to $150 on top of the per-yard price. Ordering 10% extra costs roughly $15 to $20 per yard and eliminates both risks.

Applying 10% to the patio example above: 3.0 × 1.10 = 3.3 cubic yards ordered.

What Thickness Does a Concrete Slab Need?

Thickness is determined by the load the slab will carry. Typical practice in Greater New Orleans follows three ranges, though any slab carrying structural load should be confirmed by an engineer and checked against your parish authority's requirements.

What thickness is standard for each application?

Pedestrian flatwork such as sidewalks and patios is typically poured at 4 inches. Residential driveways carrying passenger vehicles are typically poured at 4 to 5 inches. Slabs carrying heavy vehicles such as delivery trucks or equipment are typically poured at 6 inches or more.

South shore parishes sit on soft alluvial clay and organic silt, which compresses under load more than sandy soils do. Contractors working in Orleans, Jefferson, and St. Bernard parishes routinely add 1 inch to thickness recommendations that apply elsewhere, because the subgrade provides less resistance. A residential driveway that would be poured at 4 inches in a northern suburb is more commonly poured at 5 inches here.

What Do Concrete Materials Cost in 2026?

Delivered ready-mix concrete in the Greater New Orleans area runs $155 to $195 per cubic yard in 2026, depending on mix design, supplier, and delivery distance. A 3500 PSI mix standard for residential flatwork sits in the middle of that range. High-early or fiber-reinforced mixes run toward the top.

What is a short-load fee and when does it apply?

Ready-mix trucks carry 8 to 10 cubic yards at full load. Orders below 7 cubic yards trigger a short-load fee of $75 to $150 because the truck runs at a loss on delivery cost per yard. Most small patios and garage pads fall under 7 yards and pay this fee. Factor it in before comparing supplier quotes, because the per-yard rate alone understates the cost on small jobs.

What Are the Most Common Mistakes When Using a Concrete Calculator?

The four mistakes that produce a wrong volume figure are measuring the excavation instead of the finished slab, forgetting the thickened edge beam, ignoring the fall built in for drainage, and ordering to the exact calculated figure with no waste allowance.

Excavations run 6 to 12 inches larger on each side than the finished slab to allow form work. Measuring the hole adds 10 to 20% to the area. Thickened edge beams on monolithic slabs run 8 to 12 inches deep at the perimeter while the interior stays at 4 inches; the extra depth adds real volume that a simple length-times-width calculation misses. A 1% fall per foot for drainage across a 12-foot-wide slab means one edge is 1.4 inches lower than the other, which changes the average thickness slightly. None of these differences are large individually, but stacking them produces an order that is off by half a yard or more on a typical residential pour.

The calculator above gives a material estimate based on the dimensions you enter. A site visit from a concrete contractor gives an installed price that accounts for subgrade condition, reinforcement, demolition, access, and finish. Use both before committing to a project budget.