utility calculator
Estimate concrete volume, bags, and project needs.
Save this page to estimate concrete material orders on site or during project planning.
Concrete needed
3.26 yd3
Formula
Volume = length x width x depth; Cubic yards = cubic feet / 27Slab dimensions are converted into cubic feet, adjusted for waste, then converted into cubic yards and estimated bag counts.
Step by step
Example
A 20 x 12 ft slab at 4 inches thick with 10% waste needs about 3.26 cubic yards of concrete.
Related guides
Guide
Calculate concrete volume for slabs, columns, beams, and footings. Learn yardage estimation, mix ratios, and material waste factors for construction projects.
Guide
Learn unit conversion methods including metric to imperial, scientific unit prefixes, dimensional analysis, and conversion factors for length, mass, volume, and temperature.
Summary
Concrete Volume
3.26 yd3
80 lb Bags Required
147
Net Volume Needed
2.96 yd3
Waste Volume Portion
0.3 yd3
D3 visualization
Compare net material required vs. extra waste allowance.
D3 visualization
Total volume vs. estimated 80lb pre-mixed bags needed.
Guide
Concrete is ordered and poured in cubic yards. To estimate concrete needs, you must calculate the volume of the slab in cubic feet (Length x Width x Depth in feet) and convert it to cubic yards (dividing by 27).
Adding a waste allowance (typically 5% to 10%) is recommended to cover spills, uneven subgrades, and settling, preventing shortfalls during the pour.
Cubic yard
A unit of volume equal to a cube with one-yard sides, equal to 27 cubic feet; the standard unit for concrete ordering.
Waste allowance
An extra percentage added to a material estimate to cover waste, spills, or dimensions variations.
Ground subgrades are rarely perfectly flat, and concrete settles or spills during placing. A 10% waste allowance is standard practice to ensure you do not run out of material mid-pour.
It takes approximately forty-five 80-pound bags of pre-mixed concrete to fill one cubic yard of volume.