Concrete Slab Calculator
Total Volume Required:
0 Cubic Yards
Volume in Cubic Feet:
0 Cubic Feet
Premix Bags (80lb):
0 Bags
Premix Bags (60lb):
0 Bags
How to Calculate Concrete for Slabs
Planning a new patio, driveway, or shed foundation requires precise measurements to ensure you order enough concrete without overspending. The concrete slab calculator above helps you determine exactly how much material you need by converting your specific dimensions (length, width, and thickness) into total volume (cubic yards) and estimated bag counts.
The Formula:
To find the volume of concrete, multiply Length (feet) × Width (feet) × Thickness (feet).
Note: Since thickness is usually measured in inches, you must divide the inches by 12 to convert to feet first.
To find the volume of concrete, multiply Length (feet) × Width (feet) × Thickness (feet).
Note: Since thickness is usually measured in inches, you must divide the inches by 12 to convert to feet first.
Understanding Concrete Measurements
Concrete is typically sold in two ways depending on the size of your project:
- Cubic Yards: Used for ordering ready-mix trucks. One cubic yard is equal to 27 cubic feet. If your project requires more than 1.5 to 2 cubic yards, ordering a truck is often more economical and labor-efficient than mixing bags by hand.
- Pre-Mix Bags: Sold in hardware stores, typically in 60lb or 80lb sacks. These are ideal for small walkways, post holes, or small pads.
Why Include a Waste Factor?
Professional contractors always include a "waste factor" or safety margin in their calculations, typically between 5% and 10%. This accounts for several variables encountered on the job site:
- Uneven Subgrade: If the ground isn't perfectly flat, some areas of the slab will be thicker than others, consuming more concrete.
- Spillage: Minor amounts of concrete are often lost during the pouring and screeding process.
- Form Bowing: Wooden forms can bow slightly outward under the weight of wet concrete, increasing the total volume.
Standard Slab Thicknesses
Choosing the right thickness is vital for the durability of your slab:
- 4 Inches: Standard for residential sidewalks, patios, and shed bases.
- 5-6 Inches: Recommended for driveways or floors that will hold heavy vehicles.
- 6+ Inches: Heavy-duty commercial applications or areas with very poor soil conditions.