How Many Bags of Concrete Do I Need?
Calculating the right number of concrete bags for your project ensures you don't run out during a crucial pour. The amount of concrete required depends on the volume of your project in cubic feet.
Use our Concrete Calculator for an exact estimate, or follow the steps below.
Step 1: Find the Volume in Cubic Feet
Measure your slab's length, width, and thickness in feet.
Volume = Length (ft) × Width (ft) × Thickness (ft)
For example, a 10 ft by 10 ft patio that is 4 inches (0.33 ft) thick:
10 × 10 × 0.33 = 33 cubic feet
Step 2: Divide by the Bag Yield
Pre-mixed concrete bags don't yield their exact weight in volume. You must use the manufacturer's yield:
- 80 lb bag: Yields ~0.60 cubic feet
- 60 lb bag: Yields ~0.45 cubic feet
- 50 lb bag: Yields ~0.375 cubic feet
- 40 lb bag: Yields ~0.30 cubic feet
For our 33 cubic foot patio using 80 lb bags:
33 ÷ 0.60 = 55 bags
Step 3: Add Waste Factor
Always add a 5% to 10% waste factor for spillage, uneven grades, and form bowing. For 55 bags, ordering 60 bags is the safest bet.