Concrete Slab & Footing Calculator
0% (Exact)
5% (Recommended for Pro)
10% (Recommended for DIY)
15% (Complex Shapes)
Cubic Yards Needed
0
Order volume from ready-mix truck
Cubic Feet
0
Pre-Mix Bags (80 lb)
0
Approx. yield: 0.60 cu. ft. per bag
Pre-Mix Bags (60 lb)
0
Approx. yield: 0.45 cu. ft. per bag
How to Calculate Concrete for Your Project
Whether you are pouring a driveway, a patio, or a shed foundation, calculating the correct amount of concrete is critical. Ordering too little can result in a structural "cold joint" that weakens the slab, while ordering too much wastes money.
The standard formula for calculating concrete volume is:
- Length (ft) × Width (ft) × Thickness (ft) = Cubic Feet
- Cubic Feet ÷ 27 = Cubic Yards
Note that thickness is usually measured in inches, so you must divide the inches by 12 to convert it to feet before multiplying.
Why Include a Waste Margin?
Professional contractors always include a safety margin—typically 5% to 10%. This accounts for:
- Spillage during the pour.
- Uneven subgrade (dips in the ground) that require more material to fill.
- Material remaining inside the mixer or pump.
For DIY projects using pre-mixed bags, a 10% margin is highly recommended to ensure you don't run out halfway through the job.
80lb vs. 60lb Bags
If you aren't ordering a ready-mix truck, you'll be buying bags. An 80lb bag of standard pre-mix concrete yields approximately 0.60 cubic feet of cured concrete. A 60lb bag yields about 0.45 cubic feet. While 80lb bags are more cost-effective, they are significantly heavier to lift and mix. Choose the size that fits your physical capability and project scale.