Concrete Calculator
Enter your project dimensions to estimate cubic yards and the number of 60 lb or 80 lb bags needed for slabs, footings, columns, and stairs.
Length of the area in feet.
Width of the area in feet.
Depth/thickness in inches. Standard slab depth is 4 inches.
Based on standard 80lb bag = 0.6 cu ft and 60lb bag = 0.45 cu ft. Rounded up to nearest full bag.
Learn More About Concrete Calculator
How concrete volume is estimated
Concrete planning starts with volume. The calculator uses your project dimensions to estimate cubic feet and cubic yards, which are the standard measurements used for bag counts and ready-mix ordering.
That gives you a faster starting point for slabs, columns, stairs, and footings without needing to do shape-specific math by hand.
Example slab estimate
A small patio slab that is 10 feet by 12 feet and 4 inches thick needs a little under 1.5 cubic yards of concrete. Once the volume is known, you can decide whether bagged concrete is practical or whether ready-mix delivery makes more sense.
Running the numbers before buying materials can help reduce waste and lower the risk of coming up short during a pour.
Why extra material is usually needed
Real projects rarely match the math perfectly. Uneven subgrade, spillage, form variation, and minor measurement errors can all change the amount of concrete you need on site.
Adding a modest buffer is common practice, especially when the cost of running short would delay the project or force a second mix.
Frequently Asked Questions
How much concrete do I need for a typical project?
A standard garage slab (20' x 24' x 4") requires about 5.93 cubic yards of concrete. A typical 10' x 10' patio slab (4" thick) needs roughly 1.23 cubic yards. Always add 5–10% extra to account for spillage, settling, and uneven subgrade.
What is the difference between 60 lb and 80 lb bags?
A 60 lb bag yields approximately 0.45 cubic feet (about 0.017 cubic yards) of concrete. An 80 lb bag yields about 0.60 cubic feet (0.022 cubic yards). An 80 lb bag covers slightly more area per bag but both require roughly the same number of bags for a given project — the 80 lb bag simply requires fewer individual bags to handle the same volume.
How do I calculate cubic yards from dimensions?
Measure the length, width, and depth in feet. Multiply them together (L × W × D) to get cubic feet. Then divide by 27 (because 1 cubic yard = 27 cubic feet). For inches, convert to feet first by dividing by 12.
Should I order ready-mix or use bags?
For projects larger than a few cubic yards — like most driveways, foundations, or large slabs — ordering ready-mix concrete from a supplier is cheaper and more practical. Bagged concrete (60 or 80 lb bags) is best for footings under fence posts, small repairs, steps, or any project under about 4 cubic yards.