Free Concrete Calculator Online
Use this free concrete calculator to find out how much concrete you need for slabs, footings, columns, and other projects. Enter the shape and dimensions, and the concrete calculator shows the total volume in cubic yards, cubic feet, and the number of 40, 60, and 80 lb bags required.
Concrete Needed
Enter dimensions
How the Concrete Calculator Works
The concrete calculator computes volume using standard geometric formulas. For rectangular slabs: Volume = Length x Width x Depth. For cylindrical columns: Volume = Pi x radius² x height. All dimensions are converted to feet before calculation, then the result is expressed in cubic feet and cubic yards.
Once the volume is known, the concrete calculator divides by the coverage of each bag size. An 80 lb bag yields roughly 0.6 cu ft of mixed concrete, a 60 lb bag yields 0.45 cu ft, and a 40 lb bag yields 0.3 cu ft. The concrete calculator rounds up to whole bags since you cannot buy partial bags.
For projects requiring more than about 1 cubic yard, consider ordering ready-mix concrete instead of bags. The concrete calculator helps you make this decision by showing the total volume prominently. A typical concrete truck delivers 8-10 cubic yards.
Bag Coverage Reference
The concrete calculator uses these standard coverage values.
Concrete Project Tips
Order Extra
Always add 5-10% for waste. Uneven ground, spillage, and form imperfections eat into your calculated volume. The concrete calculator gives the theoretical minimum — real projects need more.
Proper Thickness
4 inches for walkways, 5-6 for driveways, 6+ for heavy loads. Cutting thickness by 1 inch saves material but risks cracking. Use the concrete calculator to compare costs at different depths.
Curing Time
Concrete reaches 70% strength in 7 days and full strength in 28 days. Keep it moist for the first 7 days. The concrete calculator helps you plan material quantities so you can focus on proper curing.
Frequently Asked Questions
Disclaimer: This concrete calculator provides estimates for planning purposes. Actual material needs may vary based on ground conditions, form accuracy, and waste. Consult a contractor for large projects.
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