Concrete Calculator
Estimate concrete for rectangular slabs or footings and round columns. Enter slab length and width in feet with depth in inches, or column diameter and height in feet, then specify identical-piece quantity and waste allowance.
Concrete Calculator tool
About the Concrete Calculator
Results include cubic feet, cubic yards, cubic meters, and alternative counts of 40-, 60-, and 80-pound premix bags. The default 10% waste allowance is adjustable; verify measurements, bag yields, and supplier ordering increments before buying.
How Is Concrete Calculated?
Use the dimensions and definitions below. Calculations use unrounded intermediate values; displayed results are rounded.
Slab cubic feet = length ft × width ft × depth in ÷ 12
Column cubic feet = π × (diameter ft ÷ 2)² × height ft
Order volume = volume per piece × quantity × (1 + waste percent ÷ 100)
Cubic yards = cubic feet ÷ 27; bags = round up(cubic feet ÷ yield per bag)
Example
A 10 ft × 10 ft slab at 4 in depth needs 33.333333 cubic feet, or 1.234568 cubic yards: approximately 1.23 cubic yards before waste.
How to Use the Concrete Calculator
- Choose slab/footing or round column.
- Enter dimensions in the labeled units.
- Enter the whole-number quantity of identical pieces.
- Set the waste allowance, initially 10%.
- Compare bulk volumes and alternative bag counts.
- Verify actual conditions and manufacturer yields before ordering.
Concrete Calculator Examples
Slab before waste
A 10 ft × 10 ft slab at 4 in depth needs 33.333333 cubic feet, or 1.234568 cubic yards: approximately 1.23 cubic yards before waste.
Slab with allowance
Adding 10% to that slab gives 36.666667 cubic feet or 1.358025 cubic yards. At 0.60 cubic foot per 80 lb bag, round 61.111111 bags up to 62.
Measurement and input conventions
A 40 lb bag yields 0.30 cubic foot, a 60 lb bag 0.45 cubic foot, and an 80 lb bag 0.60 cubic foot. Verify the product label.
No. Each count is a complete alternative using one bag size, rounded up to a whole bag.
Using the result responsibly
No. This is a volume estimate, not structural design advice. Mix strength, reinforcement, foundations, and local code requirements need separate assessment.
Keep adequate precision when transferring results to another calculation. Rounding a displayed result too early can change a later answer.
Frequently Asked Questions
What bag yields are assumed?
A 40 lb bag yields 0.30 cubic foot, a 60 lb bag 0.45 cubic foot, and an 80 lb bag 0.60 cubic foot. Verify the product label.
Are bag counts meant to be combined?
No. Each count is a complete alternative using one bag size, rounded up to a whole bag.
Does waste apply to every piece?
Yes. The total geometric volume is multiplied by one plus the waste percentage.
Is the column input a radius?
No. Enter diameter in feet. The formula divides it by two to find radius.
Does this specify structural strength?
No. This is a volume estimate, not structural design advice. Mix strength, reinforcement, foundations, and local code requirements need separate assessment.