Getting the right amount of concrete means you finish the pour without running short or wasting money on excess bags. This calculator handles slabs, footings, and post holes, giving you the volume in cubic yards or number of pre-mix bags.
Slab Dimensions
ft
ft
in
Slab
Scenario: You're pouring a 10 ft x 12 ft patio slab that's 4 inches thick.
Result: Volume is 10 x 12 x 0.333 = 40 cu ft, or about 1.5 cubic yards. That's 89 bags of 60 lb pre-mix or 67 bags of 80 lb pre-mix.
Footing
Scenario: You're pouring a continuous footing that runs 40 ft long, 12 inches wide, and 8 inches deep.
Result: Volume is 40 x 1 x 0.667 = 26.7 cu ft, or about 1.0 cubic yard. That's 60 bags of 60 lb pre-mix or 45 bags of 80 lb pre-mix.
Post Hole
Scenario: You're setting 6 fence posts in holes that are 10 inches in diameter and 36 inches deep.
Result: Each hole is about 1.64 cu ft (pi x 0.417 ft x 0.417 ft x 3 ft). Six holes total 9.8 cu ft, or 0.4 cubic yards. That's 22 bags of 60 lb pre-mix or 17 bags of 80 lb pre-mix.
At the standard 4-inch thickness, a 10x10 slab requires 1.24 cubic yards of concrete. That's about 56 bags of 80 lb pre-mix or 75 bags of 60 lb. For a 6-inch slab (garage floor), you'd need 1.85 cubic yards.
An 80 lb bag of pre-mix concrete yields about 0.6 cubic feet. Divide your total cubic feet by 0.6 to get the number of bags. For small projects (under 1 cubic yard), bags are practical. For anything larger, order a ready-mix truck -- it's faster and cheaper.
4 inches for patios and walkways. 6 inches for garage floors and driveways. 8 inches or more for heavy equipment pads. These are minimums -- check local building codes for your specific application.
Yes, order 5-10% extra. Ground is never perfectly level, forms can bow slightly, and you don't want to come up short in the middle of a pour. Running out of concrete mid-pour creates a weak cold joint.
Want to learn more before you start your project?
Read the full guide →
All Calculators
