Concrete Slab Calculator
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How to Calculate Concrete for a Slab
Planning a concrete project requires precise measurements to ensure you order enough material without excessive waste. Whether you are pouring a patio, a driveway, or a simple shed foundation, understanding how to calculate the required volume is the first step.
The Concrete Formula
Concrete is sold by volume, typically in Cubic Yards (often just called "yards"). The basic formula to determine the volume of a rectangular slab is:
Volume = Length × Width × Thickness
However, since length and width are usually measured in feet, and thickness in inches, you must convert the thickness to feet first:
- Thickness in Feet = Thickness in Inches ÷ 12
- Cubic Feet = Length (ft) × Width (ft) × Thickness (ft)
- Cubic Yards = Cubic Feet ÷ 27
Typical Thicknesses for Projects
- 4 Inches: Standard for residential sidewalks, patios, and garage floors for cars.
- 5-6 Inches: Recommended for driveways holding heavier vehicles (trucks, RVs) or shed bases.
- 6+ Inches: Heavy-duty industrial floors or commercial applications.
Bags vs. Ready-Mix Truck
Once you have your calculation, you need to decide how to buy the concrete.
Pre-Mixed Bags
Best for small projects requiring less than 1 cubic yard. You can buy these at local hardware stores in 60lb or 80lb bags.
Rule of thumb: It takes roughly 45 bags (60lb) or 34 bags (80lb) to make 1 cubic yard of concrete.
Ready-Mix Truck
If your calculator shows you need more than 1 or 2 cubic yards, ordering a Ready-Mix truck is usually more cost-effective and saves immense physical labor. Most companies have a minimum order (often 1 yard) and may charge a "short load fee" for small orders.