Concrete Calculator
Concrete Calculator
Calculate concrete volume, cubic yards, cubic meters and common bag quantities for slabs, footings, walls and round columns.
How Much Concrete Do I Need?
To estimate concrete, measure the length, width and thickness of the area you plan to pour. The calculator converts those measurements into volume and then adds the waste allowance you select.
How the Concrete Calculation Works
For rectangular slabs, footings and walls, the calculator uses:
Volume = Length × Width × Thickness
For a round column or pier, the calculator uses the cylinder formula:
Volume = π × Radius² × Height
After the base volume is calculated, the selected waste allowance is added. This extra material can help account for uneven excavation, small measurement errors, spills and concrete left in mixing equipment.
Common Concrete Bag Yields
Concrete mix manufacturers can have slightly different yields. For estimating purposes, this calculator uses these common approximate values.
| Bag Size | Approximate Yield | Approx. Bags per Cubic Yard |
|---|---|---|
| 40 lb | 0.30 ft³ | 90 bags |
| 60 lb | 0.45 ft³ | 60 bags |
| 80 lb | 0.60 ft³ | 45 bags |
Example Concrete Calculation
Suppose you are pouring a slab that measures 12 feet long, 10 feet wide and 4 inches thick.
The project volume is about 40 cubic feet, or approximately 1.48 cubic yards before waste.
With a 10% waste allowance, the recommended quantity is about 1.63 cubic yards.
Bagged Concrete vs Ready-Mix
Bagged concrete is often practical for fence posts, steps, repairs and other smaller pours. Once a project requires many dozens of bags, ready-mix delivery can become more practical.
Ready-mix pricing can also include delivery minimums, short-load charges and local fees, so compare the total project cost instead of only the material price.
How Much Extra Concrete Should I Order?
There is no single waste percentage that fits every project. A simple slab with accurate forms may require only a modest allowance. Irregular excavation, complicated shapes or difficult placement can justify more.
Frequently Asked Questions
One cubic yard contains 27 cubic feet.
Using an approximate yield of 0.60 cubic feet per bag, one cubic yard requires about 45 bags.
Yes. Switch the calculator to Metric to enter dimensions in meters, centimeters or millimeters and view the result in cubic meters.
No. Ten percent is a convenient planning allowance, but the appropriate amount depends on the project and measurement accuracy.