Square Foot Calculator for Concrete
Calculate area, volume, and bags of concrete needed for slabs, patios, driveways, and foundations.
How to Calculate Concrete Volume
Concrete is ordered and sold by the cubic yard. To calculate how much you need:
- Calculate the surface area in square feet (Length × Width).
- Convert depth from inches to feet (divide by 12).
- Multiply area × depth to get cubic feet.
- Divide by 27 to convert to cubic yards (27 cu ft = 1 cu yd).
Standard Concrete Depths
- Sidewalks & patios: 4 inches
- Driveways: 5–6 inches
- Garage floors: 6 inches
- Foundations: 8–12 inches
Bags vs. Ready-Mix
For small projects, 80 lb bags of concrete are practical — each yields about 0.6 cubic feet. For larger pours (over 1 cubic yard), ordering ready-mix from a truck is more cost-effective.
Concrete Project Thickness Guide
The correct slab thickness depends on the load the concrete must support. Choosing the wrong thickness can result in cracks or structural failure. Use this guide before entering your depth in the calculator.
| Application | Recommended Thickness | Notes |
|---|---|---|
| Residential sidewalk / walkway | 4 inches | Standard pedestrian load |
| Residential driveway | 4–5 inches | Passenger vehicles |
| Heavy-use driveway / RV pad | 6 inches | Heavy vehicles, SUVs, trailers |
| Patio / backyard slab | 4 inches | Light outdoor furniture |
| Garage floor | 4–6 inches | Vehicles + storage loads |
| Commercial floor | 6–8 inches | Forklifts and heavy equipment |
| Foundation / structural slab | 8–12+ inches | Requires engineering design |
Ready-Mix Concrete Ordering Guide
Concrete is ordered from a ready-mix supplier in cubic yards. Use this formula to convert your slab volume from cubic feet to cubic yards, and add a 10 % overage to account for spills, uneven subgrade, and settling.
PSI Strength Grades
When ordering ready-mix, specify the compressive strength in PSI (pounds per square inch):
- 2,500 PSI: Interior floors, light-duty patios
- 3,000 PSI: Standard driveways, sidewalks, slabs (most common residential)
- 3,500 PSI: High-traffic driveways, structural footings
- 4,000+ PSI: Commercial floors, structural columns, high-load applications
Bagged Concrete vs Ready-Mix: Which to Choose?
For small projects you can mix your own concrete with bagged dry mix. For larger pours, ordering ready-mix from a truck is more cost-effective and ensures consistent strength.
| Project Size | Best Option | Approximate Cost |
|---|---|---|
| Under 0.5 cubic yards (~14 cu ft) | Bagged concrete (80 lb bags) | $5–8 per 80 lb bag |
| 0.5 – 1 cubic yard | Bagged or mini ready-mix | $200–400 per cubic yard delivered |
| 1 cubic yard and above | Ready-mix truck | $125–200 per cubic yard + delivery |
Tip: One 80 lb bag of standard concrete mix yields approximately 0.60 cubic feet. Divide your total cubic feet by 0.60 to get the number of bags needed.
All Square Foot Calculators
Choose a specialized calculator for your specific project type.
Frequently Asked Questions
A 10×10 ft slab at 4 inches deep needs about 1.23 cubic yards or ~56 bags of 80 lb concrete (each bag makes 0.6 cu ft).
For patios and sidewalks, 4 inches is standard. Driveways should be 5-6 inches. Garage floors and heavy-load areas need 6+ inches.
Yes, order 5-10% more than calculated to account for uneven ground, spillage, and slight variations in depth.
There are 27 cubic feet in 1 cubic yard (3×3×3=27). Concrete is sold by the cubic yard, but calculations often start in cubic feet.