Concrete Slab Calculator
Calculate concrete volume in cubic yards, bags needed, rebar requirements, and gravel base for your patio, driveway, or garage floor slab.
How to Use This Calculator
Calculate concrete slab materials accurately:
- Enter the length and width of your slab in feet
- Select thickness based on intended use (4 inch patio, 6 inch driveway)
- Choose the slab application type for appropriate recommendations
- Check rebar option if you want reinforcement calculations
- Review concrete volume, bag count, gravel, and rebar needs
Why This Matters
Accurate concrete slab calculations prevent costly mistakes. Ordering too little means a cold joint if the truck leaves and returns, while ordering too much wastes expensive material. Understanding thickness requirements prevents premature failure.
- Calculate cubic yards with 10% overage built in
- Get bag count alternatives for small projects
- Know rebar and wire mesh requirements
- Estimate gravel base and form board needs
Worked Examples
12×20 Foot Patio Slab
4 inch thick patio with wire mesh reinforcement
Calculation: 12 × 20 × (4/12) = 80 cu ft = 2.96 cu yards
Result: 3.3 cu yards (with overage), 5 mesh sheets, 1.2 tons gravel
Driveway Slab
10×20 foot driveway, 6 inches thick with rebar
Calculation: 10 × 20 × (6/12) = 100 cu ft = 3.7 cu yards
Result: 4.1 cu yards, #4 rebar at 12 inch centers, 1.5 tons gravel
Common Mistakes to Avoid
- Underestimating material needs (always add 10% overage)
- Not compacting gravel base (causes settlement)
- Forgetting to slope for drainage (1/8 inch per foot minimum)
- Removing forms too soon (wait 24-48 hours)
- Setting rebar on ground instead of supporting mid-slab with chairs