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How to Calculate Concrete for Slabs
Planning a patio, driveway, or walkway requires precise measurements to ensure you order enough material without overspending. This Concrete Slab Calculator helps you determine exactly how much ready-mix concrete or premix bags you need for your project.
The Concrete Formula Explained
To calculate the volume of concrete required for a slab, you need to find the cubic footage of the area and then convert it to cubic yards, which is the standard unit for ordering from a ready-mix truck.
The basic formula used is:
- Step 1: Multiply Length (ft) × Width (ft) to get the square footage.
- Step 2: Convert the thickness from inches to feet by dividing by 12.
- Step 3: Multiply the Square Footage × Thickness (ft) = Cubic Feet.
- Step 4: Divide Cubic Feet by 27 to get Cubic Yards.
Recommended Thicknesses
The thickness of your slab depends heavily on its intended use:
- 4 Inches: Standard for walkways, patios, and residential shed bases.
- 5-6 Inches: Recommended for driveways and areas accommodating passenger vehicles.
- 8+ Inches: Necessary for heavy machinery or commercial foundations.
Pre-mix Bags vs. Ready-Mix Truck
If your project requires less than 1 cubic yard (about 45 bags of 80lb premix), it is often more economical to mix it yourself. For projects exceeding 2 cubic yards, ordering a ready-mix truck is usually more time-efficient and ensures a consistent cure across the entire slab.
Always include a waste margin (typically 5-10%) to account for uneven subgrades and spillage during the pour.