How Much Does a Yard of Concrete Weigh?

Why Does a Cubic Yard of Concrete Weigh What It Does?

Concrete is a composite of four materials: Portland cement, coarse aggregate (crushed stone or gravel), fine aggregate (sand) and water. Each component has its own density, and the proportions in the mix design determine the final weight per cubic yard.

Portland cement weighs approximately 94 pounds per cubic foot. Crushed limestone aggregate runs 85 to 100 pounds per cubic foot. Sand runs 90 to 100 pounds per cubic foot. Water weighs 62.4 pounds per cubic foot. A standard mix design for 3,500 PSI concrete combines these at roughly a 1:2:3 ratio by volume, cement to sand to aggregate, with a water-to-cement ratio of 0.45 to 0.50. That combination lands the finished cubic yard at 3,900 to 4,050 pounds.

The mix is not 100 percent solid. Entrapped air accounts for 1 to 3 percent of the volume in a standard mix and 4 to 8 percent in an air-entrained mix used for freeze-thaw exposure. Higher air content reduces weight slightly, shaving 30 to 80 pounds per cubic yard.

How Do Different Mix Designs Change the Weight?

Mix design is the primary variable. Three common mix categories each carry a different weight range.

Standard ready-mix concrete at 3,000 to 4,000 PSI, the mix used for driveways, patios and flatwork, weighs 3,900 to 4,050 pounds per cubic yard. High-strength mixes at 5,000 to 8,000 PSI use a lower water-to-cement ratio and a higher cement content, which pushes the weight to 4,000 to 4,200 pounds per cubic yard because the denser paste fills more voids.

Lightweight concrete uses expanded shale, clay or slate as the coarse aggregate. These materials have a dry unit weight of 25 to 55 pounds per cubic foot compared to 85 to 100 pounds for crushed stone. The result is a mix that weighs 2,400 to 2,900 pounds per cubic yard, used where structural dead load is a design constraint.

Heavyweight concrete for radiation shielding or ballast uses barite or magnetite aggregate with a unit weight above 130 pounds per cubic foot. A cubic yard of heavyweight concrete can reach 5,500 to 6,000 pounds.

How Do You Calculate the Weight of a Specific Slab?

Calculate the weight of a concrete slab in four steps: find the volume in cubic feet, convert to cubic yards, then multiply by the weight per cubic yard.

Worked example for a 400 square foot driveway at 4 inches thick:

1. Convert thickness to feet: 4 inches divided by 12 equals 0.333 feet.
2. Find volume in cubic feet: 400 square feet multiplied by 0.333 feet equals 133 cubic feet.
3. Convert to cubic yards: 133 divided by 27 equals 4.93 cubic yards.
4. Multiply by unit weight: 4.93 cubic yards multiplied by 4,000 pounds equals 19,720 pounds, or roughly 9.9 tons.

For a 6-inch slab at the same 400 square feet, the volume rises to 200 cubic feet, or 7.4 cubic yards. At 4,000 pounds per cubic yard, total weight is 29,600 pounds, approximately 14.8 tons. The 2-inch increase in thickness adds roughly 50 percent more weight and more than 50 percent more concrete cost.

Always add 5 to 10 percent to the calculated volume before ordering. Subgrade irregularities, waste at form edges and the inability to order a fraction of a yard from most batch plants mean that ordering exact volume almost always results in a short pour.

Does Fresh Concrete Weigh More Than Cured Concrete?

Fresh concrete weighs 40 to 80 pounds more per cubic yard than fully cured concrete, because the mix water that evaporates or reacts chemically during hydration is present as liquid at the time of the pour. A cubic yard of fresh 3,500 PSI concrete typically weighs 3,960 to 4,100 pounds on the truck. After the 28-day cure cycle, the same cubic yard weighs 3,900 to 4,050 pounds.

This difference matters when calculating the live load on formwork or shoring. Formwork for a 10-inch elevated slab must carry the weight of fresh concrete, not cured concrete. A structural engineer sizes shoring to the fresh weight, not the finished slab weight.

What Are the Common Calculation Mistakes and What Do They Cause?

Four mistakes account for most ordering errors and structural miscalculations on residential and light commercial pours.

The first mistake is confusing cubic yards with square yards. A square yard is a 2-dimensional measurement of area, 9 square feet. A cubic yard is volume, 27 cubic feet. Dividing slab area in square yards by slab thickness in inches does not produce cubic yards. Use cubic feet as the intermediate unit, then divide by 27.

The second mistake is forgetting to add waste. A pour calculated at exactly 5.00 cubic yards should be ordered at 5.3 to 5.5 cubic yards. Running short means a cold joint in the slab, a structural defect that causes cracking along the joint line within 2 to 5 years in most climates.

The third mistake is applying residential slab weight assumptions to structural applications. A 4-inch residential slab weighs roughly 50 pounds per square foot. A 6-inch slab weighs roughly 75 pounds per square foot. Using either number for an elevated deck or a parking structure without an engineer's review is a code violation in most jurisdictions, not a conservative design choice.

The fourth mistake is ignoring the difference between air-entrained and non-air-entrained mixes when calculating weight for load purposes. The 30 to 80 pound per cubic yard difference is small for volume ordering but meaningful when calculating total dead load on a footing or foundation system sized to close tolerances.

Is This Calculation Different for Projects in Greater New Orleans?

The weight calculation does not change, but two local conditions change how that weight behaves once the slab is on the ground. The south shore of Greater New Orleans sits on soft alluvial clay and organic silt with a high water table, often within 18 to 36 inches of the surface. A 4-inch residential slab over poorly consolidated fill generates the same 50 pounds per square foot as anywhere else, but that load is distributed onto a subgrade with a very low bearing capacity.

In practice, slabs on undisturbed native soil in Orleans, Jefferson and St. Bernard parishes often require a 4 to 6 inch compacted limestone base to spread the slab load and limit differential settlement. Without that base, the slab weight concentrates on soft spots and the slab cracks within 2 to 4 years. On the north shore, sandy subgrade drains freely but can wash out under slab edges, so the total dead load of the slab is the same while the subgrade support problem is different. The weight per cubic yard is a fixed property of the mix; what changes locally is the subgrade's ability to carry it.

When Is a Concrete Volume or Weight Calculation a DIY Task?

Volume and weight calculations for ordering concrete on a standard flatwork project, a driveway, sidewalk or patio poured on grade, are straightforward arithmetic and within any homeowner's ability. Measure the area, decide the thickness, convert to cubic yards, add 8 percent for waste and order.

A calculation becomes an engineering question when the concrete is bearing on a structure rather than on grade. Elevated slabs, parking decks, pool decks cantilevered over fill, or any slab where the dead load routes into beams, columns or footings requires a structural engineer to confirm that the support system can carry the weight of the fresh pour plus the design live load. The numbers on this page give correct unit weights, but applying those weights to a structural loading problem without a licensed professional reviewing the drawings is a risk a contractor or a homeowner should not take.

If you have a flatwork project in Greater New Orleans and want a volume estimate checked against your site conditions, a local contractor can assess the subgrade, confirm the mix specification and give you a written scope. Contact New Orleans Concrete Contractors for a site assessment and project quote.