Concrete Slab Calculator
Slab Dimensions
Cost Estimation (Optional)
Calculation Results
Total Volume Required:
0 Cubic Yards
Volume in Cubic Feet:
0 ft³
Material Options:
80lb Bags Needed (Premix):
0 Bags
60lb Bags Needed (Premix):
0 Bags
Estimated Truck Cost:
$0.00
Estimated Premix Cost (80lb):
$0.00
How to Calculate Concrete for Your Project
Planning a patio, driveway, or foundation pour requires precise volume calculations to avoid running short during the job or overspending on materials. This calculator determines the exact volume of concrete needed based on your slab's length, width, and thickness.
The Concrete Formula
Concrete is sold by the cubic yard (often just called a "yard"). To calculate this manually, use the following formula:
- Convert the thickness from inches to feet (divide by 12).
- Multiply Length (ft) × Width (ft) × Thickness (ft) to get Cubic Feet.
- Divide Cubic Feet by 27 (since there are 27 cubic feet in one cubic yard).
Example: A 10′ x 10′ patio at 4 inches thick:
10 × 10 × (4/12) = 33.33 cubic feet.
33.33 ÷ 27 = 1.23 cubic yards.
Accounting for Waste
Excavation is rarely perfect. The ground may be uneven, or forms might bow slightly under pressure. Professional contractors always add a "safety margin" or waste factor to their order.
- 5% Margin: Suitable for perfect forms on a very flat sub-base.
- 10% Margin: Recommended for most DIY projects or uneven ground.
Truck Delivery vs. Bagged Premix
Should you order a ready-mix truck or mix bags yourself?
Use Bags (Premix) if: You need less than 1 cubic yard (approx. 45-60 bags). It is labor-intensive but cost-effective for small pads, fence posts, or repairs.
Order a Truck if: You need more than 1 cubic yard. The physical effort of mixing 50+ bags by hand usually outweighs the delivery fee of a truck. Note that many concrete plants have a "short load fee" for orders under 3-4 yards.