Concrete quantity toolsConcrete quantities
Hollow cylinder volume
Calculate concrete between a round outer form and a round post or opening. Both circles must share the same center and fill height.
Enter your measurements
How it is calculated
V = π / 4 × (outer diameter² − inner diameter²) × height.
Keep the full result when using it in another calculation. Results show up to three decimal places; very small positive results use scientific notation (for example, 1e-6). No extra material for waste is added.
Measure both circles from the same center
Enter the outside diameter of the filled form and the diameter of the round post or opening that displaces concrete. Both circles must share a center, and the inner object must continue through the full fill height. Enter diameters, not radii.
The calculator subtracts the inner cylinder’s volume from the outer cylinder’s volume. A zero inner diameter means there is no round void to subtract; equal diameters leave no concrete in the modeled section.
Calculate concrete around the opening
With a 4 ft outside diameter, a 2 ft inside diameter, and a 3 ft shared height, the concrete volume is π ÷ 4 × (4² − 2²) × 3, or about 28.274 ft³.
The subtraction is valid only for the matching round cross sections and height. A square post, an off-center opening, or an object that stops partway through the form changes the geometry and should not be represented by this result.
Before you use the result
- The outer and inner circles must have the same center. The post or opening must extend through the full height entered.
- Equal inner and outer diameters give zero volume. This calculator does not cover square posts or posts that extend through only part of the fill height.