Concrete Slab Cost Calculator
Work out the cubic yards of concrete a slab needs from its area and thickness, then add your price per cubic yard and labor rate for a planning-estimate total.
Calculator
A 400 sq ft, 4-inch slab is 4.94 cubic yards of concrete ≈ $790.12 plus labor, about $2,390.12 total. Structural slabs need licensed pros and a permit.
A concrete slab is priced in two parts: the concrete itself, sold by the cubic yard, and the labor to form, pour and finish it, usually figured by the square foot. The trick that trips people up is the volume — ready-mix comes in cubic yards, but a slab is measured in square feet and inches of thickness. This calculator does that conversion for you, then multiplies by the delivered price and labor rate you enter. Nothing about local material prices is baked in; you supply those from your own quote.
It suits any flat pour where you know the footprint and thickness: a shed or garage floor, a basement slab, a patio, an equipment pad. Enter the area, pick a thickness, and the tool returns the cubic yards to order plus a total. Because the geometry never changes and every dollar is yours, the answer stays correct year after year with no maintenance.
Formula
Turn area and thickness into cubic yards, then price the concrete and add labor:
volume_cu_yd = area × (thickness_in ÷ 12) ÷ 27\ncost = volume_cu_yd × price_per_cuyd + area × labor_per_sqft
The thickness is converted from inches to feet (÷ 12), multiplied by the area to get cubic feet, then divided by 27 because there are 27 cubic feet in a cubic yard. That is the standard planning volume — order a little extra for spillage, uneven subgrade and over-dig. The labor term is a straight area × your $/sq ft; set it to 0 if you only want the material volume and cost.
Worked example
A 400 sq ft slab, 4 inches thick, with ready-mix quoted at $160 per cubic yard and finishing labor at $4 per square foot:
- Volume = 400 × (4 ÷ 12) ÷ 27 = 4.94 cu yd
- Concrete = 4.94 × $160 = $790.12
- Labor = 400 × $4 = $1,600
- Total = 790.12 + 1,600 = $2,390.12
Bump the thickness to 6 inches and the volume rises to 7.41 cu yd (concrete about $1,185), because you are pouring half again as much material. Thickness drives the concrete cost directly, which is why the reference table below is worth a look before you order.
Ordering concrete, thickness and the structural line
Always order a little extra. The 4.94 cubic yards in the example is the exact geometric volume; real subgrade is never perfectly flat, forms bulge slightly, and a bit is lost to the chute and cleanup. A common planning move is to round up and add roughly 5–10% so you are not stopping a pour a quarter-yard short — there is no good way to add fresh concrete to a slab that has started to set. Enter your own rounded volume if your supplier sells in half-yard increments.
Thickness is the big lever. Four inches is a typical planning thickness for light-duty flatwork like a patio or shed floor; heavier loads — a driveway that takes trucks, a garage, an equipment pad — often call for 5 or 6 inches, and the concrete cost rises in step because volume is linear in thickness. The right thickness, along with any reinforcing steel, control joints, vapor barrier and base preparation, depends on what the slab carries and your local code, none of which this calculator decides for you.
That is why a slab that does real structural work — a footing-supported floor, a slab tied into a foundation, anything bearing a building load — needs a licensed professional and usually a permit and inspection. Confirm the required thickness, reinforcement and base with your engineer or building department before you pour. Treat the figure here as a planning estimate for budgeting and for ordering material, not as an engineering specification or a contractor's bid.