How Many Bags of Concrete For 8×12 Slab

Estimated reading time: 4 minutes

If you’re planning to pour a concrete slab for a project like a shed, patio, or walkway, one of the critical questions is, “How many bags of concrete do I need?” In this article, we’ll guide you through estimating the number of bags required for an 8×12 slab and provide some essential tips for a successful concrete project.

8x12 double door sheds near me
8×12 double door sheds near me

Calculating the Volume of Concrete Needed

To determine how many bags of concrete you’ll need for an 8×12 slab, follow these steps:

Step 1: Measure the Dimensions:

  • Measure the length and width of the slab area. In this case, it’s 8 feet by 12 feet.

Step 2: Calculate the Area:

  • Multiply the length by the width to find the area in square feet:
    • 8 feet x 12 feet = 96 square feet

Step 3: Determine the Depth:

  • Decide on the desired thickness of your slab. Common thicknesses for residential projects range from 4 to 6 inches. For this example, let’s assume a 4-inch thick slab.

Step 4: Calculate the Volume:

  • To calculate the volume of concrete needed in cubic feet, multiply the area by the depth:
    • 96 square feet x 4/12 (convert inches to feet) = 32 cubic feet

Step 5: Convert Cubic Feet to Cubic Yards:

  • Since concrete is typically sold by the cubic yard, divide the cubic feet by 27 (the number of cubic feet in a cubic yard):
    • 32 cubic feet / 27 = approximately 1.19 cubic yards

Step 6: Account for Overages:

  • It’s advisable to order slightly more concrete than your calculated volume to account for spillage, over-excavation, or small measurement errors. Adding 10% to your calculated volume is a common practice.

Step 7: Calculate Bags of Concrete:

  • Each 80-pound bag of concrete mix typically yields about 0.6 cubic feet of concrete when properly mixed. To find the number of bags needed, divide the total cubic feet by the yield per bag:
    • 32 cubic feet ÷ 0.6 cubic feet/bag = approximately 53.33 bags

Step 8: Round Up:

  • Since you can’t purchase a fraction of a bag, round up to the nearest whole number. In this case, you’ll need approximately 54 bags of concrete.
8x12 barn
8×12 barn

Tips for a Successful Concrete Project

  1. Prepare the Site: Properly grade and compact the ground to provide a stable base for your slab. Remove any debris, rocks, or organic material.
  2. Use Reinforcement: For larger slabs or those subject to heavy loads, consider adding reinforcement like rebar or wire mesh to enhance structural integrity.
  3. Mix Concrete Consistently: Follow the manufacturer’s instructions for mixing concrete to ensure it has the right consistency and strength.
  4. Work Efficiently: Concrete can set quickly, so have all your tools and equipment ready before you begin pouring.
  5. Curing: After pouring, keep the concrete moist to prevent cracking during the curing process. Cover it with wet burlap, plastic sheeting, or use curing compounds.
8x12 double door


In conclusion, estimating the number of bags of concrete for an 8×12 slab involves straightforward calculations based on the dimensions and desired thickness of your project. However, it’s crucial to account for potential overages and round up to ensure you have enough concrete to complete the job smoothly. Adequate preparation, including site grading, reinforcement considerations, and proper mixing techniques, is essential for a successful concrete project. By following these guidelines and using our calculations, you can confidently plan your concrete project, ensuring that your 8×12 slab meets your structural and functional requirements.

By following these steps and tips, you can estimate the number of bags of concrete needed and complete your 8×12 slab project successfully.