How much a pipe segment holds, calculated from its inner diameter and length — the plumbing-specific version of a cylinder’s volume.
How it works
Halving the inner diameter gives the radius; squaring that, multiplying by pi, then by the pipe’s length gives the volume.
What this does not include
This does not include the outer or nominal pipe diameter — always use the inner (bore) diameter, since that’s what determines how much the pipe actually holds.
How to use this calculator
- Enter the pipe’s inner diameter and length.
A worked example
A pipe with 4-inch inner diameter and 120-inch length: volume = π(d/2)²×length = 1,507.9645 cubic inches.
What the variables mean
| Variable | Meaning |
|---|---|
| Inner diameter | The pipe’s internal diameter — what actually holds fluid or air, not the outer diameter including wall thickness |
| Length | Pipe length |
Edge cases worth knowing
Inner diameter, not outer diameter, determines the usable volume. Using a pipe’s outer diameter would overstate capacity, since it includes the wall thickness that holds no fluid.
A diameter of zero collapses the pipe to a line with no volume, so the calculator declines to show a result.
Frequently asked questions
Why does inner diameter matter more than outer diameter?
The pipe wall takes up space that doesn’t hold liquid — using the outer or nominal diameter would overstate the actual capacity.
What’s this most useful for?
Estimating how much water is in a length of pipe for draining, flushing, or dosing calculations.
Does pipe material affect the volume calculation?
No — the formula only depends on the inner diameter and length, regardless of what the pipe is made from.
