Concrete Slab Calculator
5% (Standard)
10% (Recommended)
15% (Complex Shapes)
80 lb bags
60 lb bags
40 lb bags
Calculation Results
Total Volume Required:
0 Cubic Yards
Volume in Cubic Feet:
0 Cubic Feet
Pre-Mix Bags Needed (80lb):
0 Bags
Estimated Material Cost:
$0.00
*Includes selected waste margin. Does not include labor or delivery fees.
How to Estimate Concrete for a Slab
Planning a driveway, patio, or shed foundation requires accurate material estimation to avoid costly shortages or unnecessary waste. This Concrete Slab Calculator helps you determine exactly how much concrete volume you need in cubic yards, as well as the number of premix bags required for smaller DIY projects.
The Concrete Formula
To calculate the concrete volume, the formula converts your slab dimensions into cubic yards, which is the standard unit for ordering ready-mix concrete.
Formula: (Length × Width × (Thickness ÷ 12)) ÷ 27 = Cubic Yards
Here is how the math breaks down:
- Step 1: Convert thickness from inches to feet by dividing by 12.
- Step 2: Multiply Length × Width × Thickness (in feet) to get Cubic Feet.
- Step 3: Divide Cubic Feet by 27 to get Cubic Yards.
Standard Slab Thickness Guidelines
Choosing the right thickness determines the structural integrity of your project:
- 4 Inches: Standard for residential sidewalks, patios, and garage floors for passenger cars.
- 5-6 Inches: Recommended for heavier vehicle driveways (trucks/RVs) or floating shed foundations.
- 6+ Inches: Heavy-duty industrial floors or areas with poor soil conditions.
Premix Bags vs. Ready-Mix Truck
Should you buy bags or order a truck? Generally, if your project requires more than 1 to 1.5 cubic yards of concrete, ordering a ready-mix truck is more cost-effective and physically manageable.
Yields for Standard Bags:
- 80lb bag: Yields approximately 0.60 cubic feet.
- 60lb bag: Yields approximately 0.45 cubic feet.
- 40lb bag: Yields approximately 0.30 cubic feet.
Don't forget to account for spill and grade unevenness by adding a 5-10% waste margin, which this calculator handles automatically.