Concrete Slab & Footing Calculator
0% (Perfect Pour)
5% (Standard)
10% (Complex Shapes)
Please enter valid dimensions (Length, Width, and Thickness).
Total Volume:
0.00 Cubic Yards
Volume in Cubic Feet:
0.00 ft³
80lb Pre-Mix Bags Needed:
0
60lb Pre-Mix Bags Needed:
0
Estimated Material Cost:
$0.00
How to Calculate Concrete for Slabs and Footings
Whether you are pouring a new driveway, a patio, or footings for a deck, accurately calculating the amount of concrete needed is crucial for your project's success and budget. Ordering too little concrete can lead to "cold joints" and structural weaknesses, while ordering too much is a waste of money.
The Concrete Calculation Formula
Concrete is measured in volume, specifically in Cubic Yards. To determine how much you need, you must first calculate the volume in cubic feet and then convert it.
The basic formula is: Length (ft) × Width (ft) × Thickness (ft) = Cubic Feet.
Since slab thickness is usually measured in inches, you must divide the inches by 12 to get feet. For example, a 4-inch slab is 0.33 feet thick.
To convert Cubic Feet to Cubic Yards, divide the total by 27 (since there are 27 cubic feet in one cubic yard).
Why Include a Waste Margin?
No pour is perfect. Professional contractors always include a safety margin or "waste factor" in their calculations. This accounts for:
- Spillage during transport or pouring.
- Uneven subgrade (dips in the ground) that require more material to fill.
- Slight variations in formwork dimensions.
We recommend a 5% safety margin for standard rectangular slabs on flat ground. For irregular shapes or uneven ground, consider adding 10%.
Pre-Mix Bags vs. Ready-Mix Truck
Should you buy bags or order a truck? This calculator provides estimates for both.
- Bagged Concrete: Best for small projects under 1 cubic yard (approx. 45 bags of 80lb mix). Ideal for setting posts or small walkways.
- Ready-Mix Truck: Best for projects over 1 cubic yard. It guarantees a consistent mix and saves you the immense physical labor of mixing dozens of bags by hand.
Standard Thickness Guide:
- 4 Inches: Standard for sidewalks, patios, and residential driveways (passenger cars).
- 5-6 Inches: Required for heavy-duty driveways (RV parking, trucks) or shed foundations.