Concrete Square Footage & Volume Calculator
Project Estimates:
Total Area: 0 sq. ft.
Volume (Cubic Yards): 0 cu. yd.
Volume (Cubic Feet): 0 cu. ft.
80lb Bags Needed: 0 bags
60lb Bags Needed: 0 bags
How to Calculate Concrete Square Footage and Volume
Planning a DIY project like a patio, driveway, or walkway requires precise measurements to avoid overspending on materials or running out of wet concrete mid-pour. Calculating concrete involves two main steps: determining the square footage of the surface and converting that into volume (cubic yards).
The Basic Concrete Formula
To calculate the amount of concrete needed, you must multiply the surface area by the depth of the slab. Since most slab depths are measured in inches, you must convert that measurement to feet to find the cubic feet, and then divide by 27 to find cubic yards.
- Step 1: Length (ft) × Width (ft) = Square Footage (Area)
- Step 2: Square Footage × (Thickness in Inches / 12) = Cubic Feet
- Step 3: Cubic Feet / 27 = Cubic Yards
Common Concrete Thickness Guide
Selecting the right thickness is critical for the structural integrity of your project:
| Project Type | Recommended Thickness |
|---|---|
| Footpaths & Sidewalks | 4 Inches |
| Residential Driveways | 5 – 6 Inches |
| RV or Heavy Truck Pads | 6 – 8 Inches |
| Shed Foundations | 4 Inches |
Example Calculation
Suppose you are pouring a driveway that is 20 feet long and 10 feet wide with a thickness of 6 inches.
- Area: 20 ft × 10 ft = 200 sq. ft.
- Volume in Feet: 200 sq. ft. × (6″ / 12″) = 100 cubic feet.
- Volume in Yards: 100 / 27 = 3.70 cubic yards.
If you were using 80lb bags of pre-mix concrete (which yield roughly 0.6 cubic feet per bag), you would need approximately 167 bags (100 / 0.6).
Ordering Tips
When ordering ready-mix concrete from a truck, it is standard practice to add a 10% margin to your total. This accounts for spillage, variations in the grade (if the ground isn't perfectly flat), and form deflection. It is much cheaper to have a little bit left over than to pay a "short load" fee for a second delivery of half a yard.