How to calculate concrete yardage
Volume in cubic feet = area in square feet x thickness in feet, so a thickness in inches is divided by 12. [1] Cubic yards = cubic feet / 27, because a cubic yard is 3 ft x 3 ft x 3 ft. For several identical pours, multiply by how many there are.
The extra covers waste. NRMCA says to order about 4% to 10% more concrete than a calculation of the plan dimensions gives, to account for waste or spillage, over-excavation and spreading of forms. [2] This calculator starts at 10%, the top of that range, and lets you change it.
A slab, pad, patio, driveway or footing is a rectangle: enter its length, width and thickness. A round pad or the base of a column is a circle: enter its diameter. A wedge or a corner piece can be a triangle. For an odd shape, calculate each part on its own and add the cubic yards.
Worked example
A 12 ft x 12 ft slab, 4 in thick: 12 x 12 x 4 / 12 = 48 cubic feet. 48 / 27 = 1.78 cubic yards. Adding 10% extra gives 1.96 cubic yards to order. At 4,000 pounds per cubic yard the pour weighs 7,111 pounds, or 3.56 tons.
How many yards of concrete do I need?
Concrete is sold by volume, in cubic yards, in its freshly mixed state as it leaves the truck mixer. [2]
Read Concrete to order above: it is the volume as measured plus your extra. Give that figure to your supplier and ask how they round it.
How many square feet does a yard of concrete cover?
One cubic yard is 27 cubic feet, so it covers 324 divided by the thickness in inches, in square feet. The second column is the other way round: the cubic yards that 100 square feet needs at that thickness.
| Thickness (in) | Square feet per cubic yard | Cubic yards per 100 square feet |
|---|---|---|
| 2 | 162 | 0.62 |
| 3 | 108 | 0.93 |
| 4 | 81 | 1.23 |
| 5 | 64.8 | 1.54 |
| 6 | 54 | 1.85 |
| 8 | 40.5 | 2.47 |
How much concrete for a 10x10 or 12x12 slab?
Square slabs 4 in thick, with and without the starting 10% extra. The thickness is an example to show the sum, not a recommendation.
| Slab | Area (ft²) | Cubic yards as measured | Cubic yards with extra |
|---|---|---|---|
| 10 x 10 ft | 100 | 1.23 | 1.36 |
| 12 x 12 ft | 144 | 1.78 | 1.96 |
| 16 x 16 ft | 256 | 3.16 | 3.48 |
| 20 x 20 ft | 400 | 4.94 | 5.43 |
| 24 x 24 ft | 576 | 7.11 | 7.82 |
How much does a yard of concrete weigh?
NRMCA says one cubic yard of concrete weighs about 4000 lb, which is 2 short tons. [2] A bagged mix can weigh a little less: QUIKRETE gives a unit weight of approximately 140 lb per cubic foot for its Concrete Mix. [3]
| Concrete | Pounds per cubic yard | Short tons |
|---|---|---|
| Ready mixed concrete (NRMCA) | 4,000 | 2.00 |
| Bagged mix (QUIKRETE unit weight) | 3,780 | 1.89 |
The calculator starts at the NRMCA figure. If your supplier gives another weight, change it under Assumptions and constants.
How many yards of concrete for a driveway?
A driveway 40 ft long and 12 ft wide, 4 in thick, is 160 cubic feet, or 5.93 cubic yards. With 10% extra that is 6.52 cubic yards. The thickness is an example to show the sum, not a recommendation. We found no source for a recommended driveway thickness, so ask your supplier or your local building authority.
How much does a yard of concrete cost?
We state no price. Ask local suppliers for a price per cubic yard, and for any delivery fee. Type your price into the optional Cost box above to see the total for the yards to order. The site does not store the prices you type.
Common mistakes and limits
- Using inches where feet belong. In the sum a 4 in thickness is 0.33 ft. The calculator converts it, and a hand sum has to.
- Ordering exactly the volume. NRMCA says to order about 4% to 10% more than the plan dimensions give. [2]
- Calling cement and concrete the same thing. Cement is the powdered ingredient that binds the aggregates together into a mass called concrete. [2]
- Taking the answer as an order. It is an estimate. Confirm the cubic yards with your supplier.
- What this tool does not cover: reinforcement, the base under a slab, formwork and how the pour is cured.
Frequently asked questions
Is concrete measured in cubic yards?
Yes. NRMCA says concrete is sold by volume, in cubic yards, in its freshly mixed state as it leaves the truck mixer. [2]
Why is concrete sold by the cubic yard?
The NRMCA publication says the volume is sold in cubic yards and worked out from the measured density of the fresh concrete. A cubic yard is 27 cubic feet, 3 ft x 3 ft x 3 ft. [2][1]
Do you calculate concrete by square feet?
Not by area alone. Multiply the area in square feet by the thickness in feet to get cubic feet, then divide by 27. One cubic yard covers 81 square feet at 4 in thick.
How much extra concrete should I order?
NRMCA says to order about 4% to 10% more concrete than a calculation of the plan dimensions gives, to account for waste or spillage, over-excavation and spreading of forms. This calculator starts at 10%, the top of that range. [2]
How do I change yards of concrete into bags?
Divide the cubic feet by the yield of one bag. QUIKRETE says an 80 lb bag yields approximately 0.60 cubic feet, so one cubic yard is 45 bags of 80 lb. Use the concrete bag calculator for your own size. [3]
Sources and references
- National Institute of Standards and Technology (NIST). NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically (SP 811, accessed November 2026). Used for: the inch and foot relationship and the 27 cubic feet in a cubic yard.
- National Ready Mixed Concrete Association (NRMCA). CIP 31, Ordering Ready Mixed Concrete (Concrete in Practice, PDF dated 2006, accessed November 2026). Used for: that concrete is sold in cubic yards, the weight of a cubic yard, and the 4% to 10% extra.
- The QUIKRETE Companies. Data Sheet, Concrete Mix, Product No. 1101-40, -50, -60, -80, -90 (revised October 2022, accessed November 2026). Used for: the unit weight of a bagged mix, and the yield of an 80 lb bag.
How we use sources: methodology.
Estimates only. Confirm quantities with your supplier. See the disclaimer. Found a wrong result? Report an error.