Concrete Calculator
Enter your slab, footing, or column dimensions to instantly calculate the cubic yards, cubic feet, and number of pre-mix bags required.
Concrete volume is length × width × thickness, with the thickness converted from inches to feet.
Use the Concrete Calculator
Dimensions
Enter thickness in inches. Common values: 4 in (patio), 6 in (driveway).
Enter the hole or tube diameter in inches.
Use this for multiple footings or columns of the same size.
Enter dimensions on the left to calculate concrete volume.
Bags Needed (with 10% buffer)
0
60 lb bags
Cubic Feet
0.00
exact
Cubic Yards
0.00
exact
Cubic Meters
0.00
exact
| Shape | — |
| Sections | — |
| Volume per section | — |
| Total volume | — |
| Volume + 10% waste | — |
| Bag yield | — |
| Bags needed | — |
Your project exceeds 1 cubic yard. Consider ordering ready-mix concrete — it is typically cheaper and faster than mixing bags at this volume.
Quick answer
Concrete volume is length × width × thickness, with the thickness converted from inches to feet. Divide cubic feet by 27 to get cubic yards. A 10 × 10 ft slab that is 4 in thick needs 33.33 cu ft (1.23 cu yd), which is 62 bags of 80 lb mix once 10% is added for waste.
Examples
| Slab | Cubic yards | 80 lb bags | 60 lb bags |
|---|---|---|---|
| 10 × 10 ft, 4 in | 1.23 | 62 | 82 |
| 12 × 12 ft, 4 in | 1.78 | 89 | 118 |
| 20 × 10 ft, 6 in | 3.70 | 184 | 245 |
Enter your dimensions for the exact volume and bag count, including round footings and columns.
Summary
This concrete calculator helps you estimate the volume of concrete needed for slabs, rectangular footings, circular footings, and columns. Enter your dimensions in inches or feet and select your preferred bag weight to get an accurate bag count with a 10% waste allowance. All math is done in your browser — no data is sent to any server.
How it works
- Select the shape: slab, rectangular footing, circular footing, or column.
- Enter the dimensions (length, width, thickness, diameter, or height) in feet and inches.
- Choose the pre-mix bag size: 40 lb, 60 lb, or 80 lb.
- Click Calculate to see the volume in cubic feet and cubic yards.
- The result shows the exact bag count plus a 10% waste buffer recommendation.
- Use the Reset button to start a new calculation.
Use cases
- Estimating concrete bags for a backyard patio or driveway slab.
- Planning material purchases for fence post footings.
- Sizing concrete volume for a sonotube column or pier.
- Checking concrete quantities before ordering a ready-mix truck.
- Budgeting material costs for a DIY home-improvement project.
- Verifying a contractor's concrete estimate.
- Teaching students or apprentices how concrete volume is calculated.
- Planning multiple pour sections and comparing shape options.