Concrete Slab Calculator

Calculate the exact amount of concrete needed for your slab project, including bags, volume, and waste factor.

Imperial
Metric
Enter total length in feet Please enter a valid length
Enter total width in feet Please enter a valid width
4 inches is standard for residential slabs Please enter a valid thickness
Add 10-15% for spillage and uneven substrate
Affects bag yield calculations
3D Slab Visualization
How to Use
  • Measure the length and width of your slab area in feet
  • Determine the thickness (4 inches is standard for residential slabs, 6 inches for driveways or heavy loads)
  • Add waste factor (10-15% recommended for most projects)
  • Select your concrete mix type based on project requirements
  • Click Calculate to see your results

Tips for accurate measuring:

  • Measure at the longest and widest points
  • Account for any irregularities in the shape
  • For sloped areas, use the average thickness
📐 Formula Used
Volume Formula:
Length (ft) × Width (ft) × Thickness (in ÷ 12) ÷ 27 = Cubic Yards
With Waste Factor:
Volume × (1 + Waste%) = Total Volume
Bag Calculations:
Cubic feet ÷ 0.30 = 40 lb bags
Cubic feet ÷ 0.45 = 60 lb bags
Cubic feet ÷ 0.60 = 80 lb bags
Weight Calculation:
Cubic yards × 4,000 lbs = Total weight

Example: For a 10 ft × 8 ft slab at 4 inches thick:

10 × 8 × (4 ÷ 12) ÷ 27 = 0.99 cubic yards
0.99 × 27 = 26.7 cubic feet
26.7 ÷ 0.45 = 60 bags (60 lb)
💡 Pro Tips
  • The Magic Number: For 4-inch slabs, divide square footage by 81 to get cubic yards
  • Always order extra: Add 10-15% to account for spillage and uneven subgrade
  • Coverage: One cubic yard covers 81 sq ft at 4 inches thick
  • Ready-mix delivery: Consider for projects over 2 cubic yards
  • Reinforcement: Add rebar or wire mesh for driveways and heavy-load areas
  • Curing time: Allow 7 days before light use, 28 days for full strength