Circular Concrete Calculator

Calculate the exact volume, weight, and number of bags needed for circular slabs, columns, and sonotubes.

Total width across center
Vertical height or thickness
Number of columns or slabs
Standard is 10% for spills
  1. Select your preferred unit system (Imperial or Metric) from the dropdown.
  2. Enter the total Diameter of your circular slab, column, or sonotube.
  3. Enter the Depth or thickness of the concrete pour.
  4. Adjust the Quantity if you are pouring multiple identical shapes.
  5. Set the Waste Margin (10% is standard for spills and over-excavation).
  6. Watch the 3D shape update in real-time as you type, and review your results below.

The volume of a circular cylinder or slab is calculated using the formula for the volume of a cylinder:
Volume = π × r² × h
Where r is the radius (half of the diameter) and h is the depth/height. The total weight is estimated by multiplying the volume by the standard density of concrete (150 lbs/cu ft or 2,400 kg/m³). Bag counts are determined by dividing the total volume by the yield of a standard bag.

  • Sonotubes: Always brace your sonotubes firmly before pouring to prevent bulging or shifting.
  • Ready-Mix vs. Bags: If your total volume exceeds 1.5 cubic yards, ordering ready-mix is usually more cost-effective and ensures a consistent pour.
  • Vibration: Use a concrete vibrator or tap the forms with a rubber mallet to release trapped air bubbles, especially in deep, narrow columns.