Concrete Project Calculator
*Estimates include the selected waste margin. Always round up when ordering. Truck delivery often has minimum order fees (e.g., short load fees) not included here.
Guide to Estimating Concrete Slab Costs
Planning a new patio, driveway, or shed foundation requires precise calculations to ensure you order enough material without overspending. Concrete is measured by volume, specifically in cubic yards, but allows for two primary purchasing methods: pre-mixed bags for smaller jobs or ready-mix truck delivery for larger projects.
How to Calculate Concrete Volume
The core formula for calculating the amount of concrete needed is:
However, since dimensions are often measured in feet and inches, conversion is necessary:
- Convert Thickness: Divide the thickness in inches by 12 to get feet.
- Calculate Cubic Feet: Multiply Length (ft) × Width (ft) × Thickness (ft).
- Convert to Cubic Yards: Divide the total cubic feet by 27 (since there are 27 cubic feet in one cubic yard).
Standard Thickness Recommendations
Choosing the right thickness is crucial for the durability of your slab:
- 4 Inches: Standard for walkways, patios, and residential garage floors (light vehicle traffic).
- 5-6 Inches: Recommended for driveways holding heavier vehicles, RVs, or heavy machinery.
- 6+ Inches: Heavy-duty commercial applications.
Bags vs. Ready-Mix Truck
When to use Pre-Mixed Bags (60lb or 80lb)
Bags are ideal for small projects requiring less than 1 cubic yard of concrete (approx. 45-50 bags of 80lb mix). While the material cost per yard is higher, you avoid delivery fees. It is labor-intensive as every bag must be mixed manually.
When to order a Ready-Mix Truck
If your project requires more than 1 cubic yard, a truck is usually more economical and significantly saves labor. Note that many suppliers have a "short load fee" for orders under 4-6 cubic yards.
Don't Forget the Waste Margin
Uneven subgrades and spillage can lead to shortages. It is industry standard to add a 5% to 10% safety margin to your total volume calculation. Running out of concrete halfway through a pour creates a "cold joint," which weakens the slab structurally and ruins the aesthetic finish.