Concrete Slab Calculator
Determine the number of 60lb or 80lb premix concrete bags and total cubic yards needed for slabs, patios, and footings. Includes waste percentage for more accurate ordering.
Complete Guide: Concrete Slab Calculator
Everything you need to know about using this tool effectively
Enter the length, width, and thickness of your concrete slab to calculate the volume needed. The calculator shows the result in cubic yards, cubic feet, and the number of 60-pound or 80-pound premix bags required. It adds a standard 10 percent waste factor to help you order the right amount without running short.
Volume is calculated as length times width times thickness, all converted to feet. Cubic yards are derived by dividing cubic feet by 27. Bag count assumes one 60-lb bag covers 0.45 cubic feet and one 80-lb bag covers 0.60 cubic feet. The 10 percent waste factor accounts for uneven subgrade, spillage, and measurement variations. One cubic yard equals 27 cubic feet or approximately 45 standard 80-lb bags.
Patio construction
Homeowners can calculate how much concrete to order for a new backyard patio.
Driveway pouring
Contractors can estimate material needs for residential driveway projects.
Footing calculations
Builders can determine concrete volume for foundation footings and grade beams.
DIY projects
Makers and hobbyists can figure out how many premix bags to buy for small projects like mailbox posts or shed pads.
Measure the slab area
Determine the length and width of the area where concrete will be poured.
Set the slab thickness
Enter the desired thickness. Standard residential slabs are 4 inches thick.
Review your concrete estimate
The calculator shows cubic yards for ready-mix orders and bag counts for premix purchases.
Standard residential slabs are 4 inches thick; driveways should be 4 to 6 inches
Order 5 to 10 percent extra beyond the calculator result to avoid running short mid-pour
For large projects, ready-mix delivery is more cost-effective than individual bags
Prepare a smooth, compacted subgrade to minimize wasted concrete filling low spots
How many bags of concrete make one cubic yard?
It takes approximately 45 bags of 80-lb concrete mix or 60 bags of 60-lb mix to make one cubic yard. The exact number depends on the specific product coverage rate.
How thick should a concrete slab be?
For patios and walkways, 4 inches is standard. Driveways should be at least 4 inches for passenger cars and 5 to 6 inches for heavier vehicles. Garage floors typically use 4 to 6 inches with reinforcement.
What is the waste factor for?
The 10 percent waste factor accounts for concrete lost to uneven subgrade, spillage during placement, over-excavation, and measurement inaccuracies. It is standard practice in the industry.
Should I order ready-mix or use premix bags?
For projects under about 1 cubic yard, premix bags are practical. For larger projects, ready-mix truck delivery is more cost-effective and saves significant labor. The calculator shows both options.
Do I need reinforcement in my slab?
Most slabs benefit from wire mesh or rebar reinforcement to control cracking. The calculator estimates concrete volume only. Consult local building codes for reinforcement requirements in your area.