Concrete Calculator
Calculate how much concrete you need for slabs, footings, columns, and steps in cubic yards and bags.
A concrete calculator estimates how many cubic yards or bags of concrete you need for slabs, footings, columns, and other projects.
Examples
10x20 ft patio, 4 inches thick
Four 12-inch round columns, 4 feet tall
Frequently Asked Questions
How much does a cubic yard of concrete weigh?
Should I use bags or order a truck?
Quick Tips
- •Always add 5-10% waste factor for slabs and 10-15% for complex shapes.
- •Concrete is sold by the cubic yard for truck delivery; one truck typically carries 8-10 yards.
- •Standard slab thickness is 4 inches for patios and 6 inches for driveways.
- •An 80 lb bag of pre-mix yields approximately 0.6 cubic feet of concrete.
A concrete calculator estimates how many cubic yards or bags of concrete you need for slabs, footings, columns, and other projects.
How to Use This Calculator
Select the project type (slab, column, or stairs), enter the dimensions, and set a waste factor percentage. The calculator computes the volume of concrete needed in cubic yards plus the number of pre-mixed bags required.
Understanding the Formula
Slab: Volume = Length x Width x Depth. Column: Volume = pi x (Diameter/2)^2 x Height. Stairs: Volume = sum of step volumes + base slab. All converted to cubic yards (1 cu yd = 27 cu ft = 46,656 cu in).
Examples
10x20 ft patio, 4 inches thick
Volume = 20 x 10 x (4/12) = 6.67 cu ft / 27 = 2.47 cu yards. With 10% waste: 2.72 cu yards.
Four 12-inch round columns, 4 feet tall
Each column = pi x 6^2 x 48 = 5,429 cu in = 0.116 cu yd. Four columns = 0.466 cu yd.
Frequently Asked Questions
How much does a cubic yard of concrete weigh?
Wet concrete weighs approximately 3,900 to 4,050 pounds per cubic yard (about 150 lbs per cubic foot).
Should I use bags or order a truck?
For projects under 1 cubic yard, pre-mixed bags are practical. For 1-3+ cubic yards, ordering from a ready-mix plant is more economical and ensures consistent quality.
Assumptions & Limitations
- Add 5-10% extra material for waste and cuts.
- Assumes standard concrete density of approximately 150 lbs per cubic foot; lightweight mixes will differ.
- Bag yield estimates are approximate; actual yield depends on mixing consistency and water ratio.