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How to Calculate Concrete Volume
Concrete volume is calculated by multiplying length times width times depth. Since depth is often measured in inches, convert it to feet by dividing by 12. The result in cubic feet is then divided by 27 to convert to cubic yards, which is how concrete is typically sold.
Concrete Bags vs Ready-Mix
For small projects, bags of premixed concrete (60 lb or 80 lb) are convenient. An 80-lb bag yields about 0.6 cubic feet. For larger projects over 1 cubic yard, ordering ready-mix from a concrete truck is more economical and provides a better finish.
Accounting for Waste
Always order 5% to 10% more concrete than calculated to account for spillage, uneven ground, and form irregularities. Running short during a pour can compromise the structural integrity of the slab.
Common Concrete Depths
Standard depths are 4 inches for sidewalks and patios, 6 inches for driveways and garage floors, and 8 to 12 inches for footings and foundations. Thicker slabs provide more strength for heavier loads.
Frequently Asked Questions
An 80-lb bag of concrete yields approximately 0.6 cubic feet when mixed. Divide your total cubic feet by 0.6 to find the number of bags needed. This calculator does that math for you automatically.
For patios and walkways, 4 inches is standard. Driveways should be at least 6 inches. Garage floors are typically 6 inches, and structural footings are 8 to 12 inches or more depending on the load requirements.
Yes. Plan for 5% to 10% extra to cover spillage, uneven subgrade, and minor form movement. For complex shapes or sloped ground, increase the waste factor to 15%.
One cubic yard equals 27 cubic feet (3 ft x 3 ft x 3 ft). Ready-mix concrete is sold by the cubic yard, while bags are measured in cubic feet. This calculator provides both units.