Concrete Calculator

How Does the Concrete Calculation Work?

The calculator uses one formula: length in feet multiplied by width in feet multiplied by depth in feet, divided by 27. The divisor 27 converts cubic feet to cubic yards, because one cubic yard equals 27 cubic feet.

What Does a Worked Example Look Like?

A driveway that is 16 feet wide, 40 feet long and 5 inches deep (0.417 feet) works out as follows: 16 × 40 × 0.417 = 266.9 cubic feet. Divide 266.9 by 27 and the result is 9.88 cubic yards. Round up to 10 cubic yards before applying the waste allowance.

Convert inches to feet before multiplying. Divide the inch measurement by 12. A 4-inch slab is 0.333 feet. A 5-inch slab is 0.417 feet. A 6-inch slab is 0.5 feet. Using inches directly in the formula produces a figure 12 times too small.

How Much Extra Concrete Should You Order?

Add 8 to 10 percent to the calculated cubic yardage on every pour. That allowance covers three predictable losses: spillage during the pour, subgrade that is slightly lower than the target depth across the full slab area, and over-excavation at the edges where the perimeter often digs wider than planned.

On the 10-cubic-yard driveway above, a 10 percent allowance adds 1 cubic yard, bringing the order to 11 cubic yards. Running short mid-pour is a serious problem. A cold joint forms where fresh concrete meets partially set material, and that joint is a permanent weak plane where cracking and water infiltration begin. Ordering a partial extra yard after the truck leaves costs a second delivery fee plus the short-load charge. Order the full amount at the start.

What Thickness Does Each Job Require?

Thickness is determined by the load the slab carries, not by preference. The values below reflect common practice in the trade. Anything structural, including slabs supporting walls or equipment, requires an engineer's specification, not a rule of thumb.

• Foot traffic only (sidewalks, patios): 4 inches over compacted base is standard practice on stable ground.
• Passenger vehicles (residential driveways): 4 inches is the national rule of thumb, but 5 inches is typical practice in Greater New Orleans because the soft alluvial clay and organic silt common across Orleans, Jefferson and St. Tammany parishes compress under load and reduce effective bearing capacity.
• Light commercial and heavy SUVs or pickups: 5 to 6 inches with reinforcement.
• Heavy vehicles, forklifts, loaded delivery trucks: 6 inches minimum, rebar or fiber reinforcement, and in most cases an engineer's review before the pour.

Confirm thickness requirements for any permitted project with the relevant parish building department before finalizing the design.

What Do Concrete Materials Cost in 2026?

Ready-mix concrete delivered in the Greater New Orleans area runs $155 to $195 per cubic yard in 2026. The range moves with the mix design, the admixtures specified and the distance from the batch plant to the site. A 3500 PSI mix sits toward the lower end of that range. A 4000 PSI mix with air entrainment or fiber reinforcement moves toward the higher end.

The cost most people miss is the short-load fee. Ready-mix plants set a minimum load, typically 3 cubic yards. An order below that minimum draws a fee of $75 to $150 on top of the per-yard price. A footing that calculates to 1.8 cubic yards does not cost 1.8 times the per-yard rate. It costs 1.8 yards of material plus the short-load charge. Factor that into any small-pour budget.

What Mistakes Make the Calculator Return the Wrong Number?

The four most common calculation errors each cause the tool to return a figure that does not match the actual pour.

• Measuring the excavation instead of the finished slab. The slab is smaller than the hole. Use the finished slab dimensions.
• Forgetting the thickened edge. Driveways and slabs-on-grade often have a perimeter footing 8 to 12 inches deep. That extra volume adds 10 to 20 percent to the total on a typical residential driveway and is not captured by a flat-depth calculation.
• Ignoring drainage fall. A patio with a 1-inch-per-8-foot slope across a 16-foot width has a depth that varies by 2 inches from one side to the other. Use the average depth, not the minimum.
• Ordering to the exact calculated figure with no waste allowance. See the 8 to 10 percent rule above.

The calculator gives a reliable material estimate based on the dimensions entered. An installed price depends on subgrade condition, reinforcement, finish, demolition of existing concrete and access to the site. A site visit produces that number.