A cubic yard of concrete is 27 cubic feet, enough for 81 square feet of slab at 4 inches. To find the yards for a pour, multiply length × width × thickness in feet and divide by 27: a 24 × 30 ft driveway 5 inches thick is 300 cubic feet, or 11.11 cubic yards. With a 10% allowance you would order 12.25 yards, which arrives as one full 10-yard truck and a short load of 2.25.
How cubic yards are calculated
Cubic yards = length (ft) × width (ft) × thickness (in) ÷ 12 ÷ 27
For the driveway: 30 × 24 = 720 sq ft; × 5 ÷ 12 = 300 cu ft; ÷ 27 = 11.11 cu yd. Add 10%: 12.22 cu yd. The calculator then rounds up to the next quarter yard, 12.25, because a plant batches in steps and a shortfall at the end of a pour is far worse than a little left over. Ask your supplier what increment they sell; some take half yards only.
In metric the result is in cubic meters: length × width × thickness in meters. One cubic yard is 0.765 m³, one cubic meter is 1.31 cubic yards.
Cubic yards per 100 square feet
| Thickness | Cubic yards per 100 sq ft |
|---|---|
| 4 in | 1.23 |
| 5 in | 1.54 |
| 6 in | 1.85 |
| 8 in | 2.47 |
These are plan volumes. Add your allowance on top.
How much extra to order
The National Ready Mixed Concrete Association (NRMCA) recommends ordering 4% to 10% more than the volume from the plan dimensions (CIP 31 and CIP 8). The reasons are ordinary: forms bulge, the subgrade is lower in places, some concrete stays in the chute and the wheelbarrow. Its example is sobering: a slab ⅛ inch thicker than the planned 4 inches is 3% short, which on a 32-yard order is a full yard. The calculator starts at 10%.
Trucks and short loads
NRMCA puts truck mixer capacity at 8 to 12 cubic yards; the calculator assumes 10 and lets you change it to what your plant sends. The bars under the result show each truck and how full it is. When the last truck, or the only one, carries less than a full load, it is a short load, and suppliers add a fee for it. HomeAdvisor's June 2026 figure is $40 to $60 per cubic yard on orders below a full truckload; Fixr (January 2025) reports $15 to $17 per yard for 1 to 5 yard orders. For the driveway's 2.25-yard second truck that could be $90 to $135.
Two ways around it: round the job up to a full truck by pouring a second slab or footing the same day, or pour a small job from bags. The concrete bag calculator shows the bag count for the same volume: at 45 bags of 80 lb per yard, 2 yards is already 90 bags.
NRMCA also advises re-checking the remaining volume near the end of a big pour and telling the plant, so the last loads can be adjusted instead of waiting for a short load after the plant has closed.
Concrete calculator for cubic yards, step by step
- Measure every part of the pour and enter each as a section: the slab, the thickened edge, the footings, a pad for the AC unit.
- Leave the allowance at 10% unless the forms are tight and the base is flat and compacted.
- Set the truck size your supplier uses.
- Read the order in yards and the truck bars, then call it in with the script under the result.
Calling in the order
NRMCA's guide to ordering lists what the plant needs from you, and the calculator fills it in: the quantity, what the concrete is for and how it will be placed, the strength, the slump, air entrainment if the concrete will freeze in service, the coarse aggregate size, and the address, access, date and time. NRMCA puts specified strengths of 3,500 to 5,000 psi as typical for most work and a slump of 3 to 5 inches for most placements, but the plant knows its local mixes: tell them the use and ask. Book well ahead and have the crew ready when the truck arrives; a loaded truck weighs about 80,000 lb and may not manage loose dirt or residential curbs, so plan where it stops or book a pump.
Next steps
Price the order with delivery, labor and pumping in the concrete cost calculator, size the rebar for the slab, or go back to the concrete calculator for other shapes. For anything else sold by the yard, use the cubic yard calculator.