Concrete Volume Calculator

Calculate the exact amount of concrete needed for your project with precision. Get instant results in cubic yards, bags, and cost estimates.

Length of slab Enter valid length
Width of slab Enter valid width
Standard: 4" residential Enter valid thickness
Number of slabs
Recommended: 10-15%
Optional cost estimate
How to Use
  1. Select your project shape from the dropdown menu above
  2. Enter dimensions in your preferred units (Imperial or Metric)
  3. Adjust waste buffer if needed (10% recommended for most projects)
  4. Optionally enter price per cubic yard/meter for cost estimate
  5. Results update automatically as you type - no need to click Calculate
  6. Download PDF report to share with suppliers or contractors

Pro Tips:

  • Standard residential slabs are 4" thick
  • For driveways, use 5-6" thickness
  • Post holes should be 3x the post diameter
  • Order ready-mix for projects over 2 cubic yards
Formula Used
Rectangular Slab:
Volume = Length × Width × (Thickness ÷ 12)
Result in cubic feet, then ÷ 27 for cubic yards
Circular Slab/Column:
Volume = π × (Diameter ÷ 2)² × (Thickness ÷ 12)
Post Hole:
Hole Volume = π × (Hole Diameter ÷ 24)² × Depth
Post Volume = π × (Post Diameter ÷ 24)² × Depth
Concrete = Hole Volume - Post Volume
Wall:
Volume = Length × Height × (Thickness ÷ 12)
Footing:
Volume = Length × (Width ÷ 12) × (Depth ÷ 12)
Steps:
Volume = Σ (Step Area × Run) for each step
Step n Area = Width × (Rise × n)

Bag Yields:

  • 40 lb bag = 0.30 cubic feet
  • 60 lb bag = 0.45 cubic feet
  • 80 lb bag = 0.60 cubic feet
Concrete Volume Tips
  • Always add extra: Order 10-15% more than calculated to account for spillage, over-excavation, and uneven subgrades
  • Ready-mix vs bags: For projects over 2 cubic yards, ready-mix concrete is more economical
  • Curing time: Concrete reaches 70% strength in 7 days, full strength in 28 days
  • Temperature matters: Avoid pouring below 40°F or above 90°F
  • Reinforcement: Add rebar or wire mesh for structural applications
  • Subgrade prep: Proper compaction prevents settling and cracking
Bag Yield Reference
Bag Size Yield (cu ft) Yield (cu yd) Best For
40 lb 0.30 0.011 Small repairs, posts
60 lb 0.45 0.017 Medium projects
80 lb 0.60 0.022 Large projects