Concrete Slab & Bag Calculator
Calculate cubic yards and premix bags needed for your project
Standard patio/walkway is 4 inches. Driveway is 6 inches.
0% (Exact)
5% (Minimal)
10% (Recommended)
15% (Safe)
Estimated Materials Needed
Total Volume Required:
0 Cubic Yards
Volume in Cubic Feet:
0 ft³
Pre-Mix Bag Options (If not ordering truck):
80lb Bags of Concrete:
0 Bags
60lb Bags of Concrete:
0 Bags
Estimated Total Weight:
0 lbs
How to Calculate Concrete for Slabs and Footings
Whether you are pouring a new patio, a driveway, or a simple shed foundation, determining the correct amount of concrete is critical. Ordering too little results in a "cold joint" and structural weakness, while ordering too much is a waste of money.
The Concrete Calculation Formula
To find the volume of concrete needed for a slab, you need to determine the volume in cubic feet and then convert it to cubic yards (which is how ready-mix trucks measure volume).
- Step 1: Measure Length (feet) × Width (feet).
- Step 2: Convert Thickness from inches to feet (divide inches by 12).
- Step 3: Multiply Length × Width × Thickness (in feet) to get Cubic Feet.
- Step 4: Divide Cubic Feet by 27 to get Cubic Yards.
Bags vs. Ready-Mix Truck
If your project requires less than 1 cubic yard of concrete, it is often more economical to mix it yourself using 60lb or 80lb pre-mix bags available at hardware stores.
Rule of Thumb:
– An 80lb bag yields approximately 0.60 cubic feet.
– A 60lb bag yields approximately 0.45 cubic feet.
Why Add a Safety Margin?
Ground preparation is rarely perfect. Excavation depths can vary by half an inch, and spillage occurs during mixing and pouring. We recommend adding a 5% to 10% safety margin to your calculation to ensure you don't run out of material mid-pour.