Estimate cubic yards and premix bags for slabs, footings, and columns—matching Concrete Network.
Project dimensions
4″ is standard for residential slabs
Volume of concrete
Tip: for a 4″ slab, yards ≈ square footage ÷ 81 (pro “magic number”).
How many pre-mix bags
Never order the exact amount—include a safety margin so you do not come up short on the jobsite.
Formula
How it works
Examples
About this calculator
The Concrete Calculator estimates cubic yards and premix bags for slabs, footings, and columns. It follows the same volume approach used by Concrete Network—length × width × thickness, converted to yards and 40/60/80 lb bag counts.
Slab, footing & column modes
Switch between residential slabs (thickness in inches), continuous footings, and round columns with diameter and height.
Yards and bag counts
See cubic yards for ready-mix orders plus 40, 60, and 80 lb bag estimates for smaller DIY pours.
Built-in planning tips
Includes the 4″ “magic number” tip (sq ft ÷ 81) and reminds you to order a safety margin so you do not come up short.
- Patios & driveways
- Footings & piers
- Garage slabs
- DIY bag estimates
Frequently asked questions
Quick answers about this calculator—how it works, accuracy, and everyday use.
Multiply length × width × thickness (convert inches to feet). Divide cubic feet by 27 to get cubic yards. For a 10×10 slab at 4 inches, that is about 1.24 cubic yards—or roughly 56 bags of 80 lb premix.
At 4 inches thick you need about 1.24 cubic yards (≈56 eighty-pound bags). At 6 inches thick you need about 1.85 yards (≈84 eighty-pound bags). Use the slab mode in this calculator for exact counts.
Pros often divide total square footage by 81 to estimate cubic yards for a 4″ pour. Example: 200 sq ft ÷ 81 ≈ 2.46 yards. Always add a safety margin so you do not run short.
Larger jobs like driveways are easier with ready-mix by the yard. Smaller projects—walkways, pads, and footings—are often practical with 40, 60, or 80 lb bags. This tool shows both yards and bag counts.