Concrete Calculator — Cubic Yards

Ready-mix concrete in the United States is sold by the cubic yard, and every supplier quote you receive will be in yards — never in square feet. The math is the same for a patio, a shed pad, a garage floor or a driveway: multiply length by width to get the area in square feet, multiply that by the thickness expressed in feet, and divide the result by 27 because a cubic yard contains 27 cubic feet.

Thickness is where most homeowners lose money. A 4 inch slab is the standard for patios, walkways and shed pads. Driveways that carry passenger cars should be poured at 5 to 6 inches, and anything carrying an RV, a delivery truck or a boat trailer should be 6 to 8 inches over a compacted base. Going from 4 inches to 6 inches raises the concrete volume by 50%, so decide on thickness before you price the job, not after.

Always add waste. Subgrade is never perfectly level, forms bow slightly under the weight of wet concrete, and the last wheelbarrow always disappears somewhere. Ten percent is the accepted allowance for a flat, well-prepared slab. Push it to 15% if you are pouring over gravel that has not been screeded, if the excavation edges are ragged, or if the pour includes thickened edges and footings.

A cubic yard takes roughly 45 bags of 80 lb pre-mix, 60 bags of 60 lb mix, or 90 bags of 40 lb mix. Each 80 lb bag yields about 0.60 cubic feet of finished concrete once mixed with water, and 27 ÷ 0.60 gives you the 45 bag figure. Many contractors quote 42 bags per yard for the higher-yield mixes, so treat 42 to 45 as the working range and round up.

Bags make sense for small work — a mailbox post, a couple of deck footings, a 4 ft × 4 ft AC pad. Once you pass about one cubic yard, roughly 45 bags, mixing by hand stops being economical in both money and labor. At that point a short-load ready-mix delivery, or a trailer mixer rented for the day, will cost less per yard and give you a far more consistent finish because the whole pour cures at the same rate.

Ready-mix suppliers price the concrete itself per cubic yard, then add fees that catch first-time buyers off guard. A short-load fee applies to any order under the truck minimum, usually 8 to 10 yards, and runs $50 to $170 per missing yard. Waiting time beyond the free window — typically 5 to 7 minutes per yard on the truck — is billed at $75 to $150 an hour. Saturday delivery, hot-weather retarders, fiber reinforcement and cold-weather accelerators are all separate line items.

Regional pricing varies more than most national averages suggest. Texas and the Southeast sit near the bottom of the range because aggregate is close to the plants and haul distances are short. California, the Pacific Northwest and the Northeast metros sit at the top because of aggregate scarcity, emissions rules and labor costs. Use the table below as a planning range, then call two local plants for a real quote before you set forms.