### Answer

To determine the number of 80 lb. bags of concrete required for a yard of concrete that is 4 inches thick, you need to convert the thickness from inches to feet and then use the appropriate conversion factors. Feel free to check out of formula's below to calculate this, or use our concrete calculator.

The Conversion:One yard of concrete is equal to 27 cubic feet (since 1 cubic yard = 3 feet × 3 feet × 3 feet = 27 cubic feet).

First, we need to find the volume of concrete required for an area of one square yard and a thickness of 4 inches. Since the area is 1 square yard, and the thickness is 4 inches (which is 4/12 = 0.333 feet), the volume can be calculated as follows:

**Volume = Area × Thickness****Volume = 1 yard² × 0.333 feet****Volume = 0.333 cubic yards**

Now, we need to convert the volume to the number of 80 lb. bags. Each bag of concrete is typically measured in cubic feet, so we'll need to convert the volume in cubic yards to cubic feet:

**1 cubic yard = 27 cubic feet****0.333 cubic yards ≈ 0.333 × 27 cubic feet****0.333 cubic yards ≈ 8.991 cubic feet**

Next, we'll find out how many 80 lb. bags are required for 8.991 cubic feet of concrete:

**Number of bags = Volume in cubic feet / Volume per bag in cubic feet****Number of bags = 8.991 cubic feet / 0.45 cubic feet (80 lb. bag)****Number of bags ≈ 19.98**

Since you can't have a fraction of a bag, you would need to round up to **20 bags of 80 lb. concrete to cover a yard of concrete that is 4 inches thick**.