What this calculator does
The volume inside a pipe is a cylinder volume calculation, but pipes are normally specified by their outer diameter and wall thickness rather than the inner diameter that actually determines how much they can hold. Subtracting twice the wall thickness from the outer diameter gives the inner (bore) diameter, and from there the internal volume follows the usual V = πr²h formula for a cylinder.
For plumbing, irrigation and tank-filling purposes, the number people actually want is capacity in litres rather than cubic metres, since that is how water and other fluids are usually measured and priced. This calculator takes outer diameter and wall thickness, works out the bore, and reports the result as both litres and cubic metres.
The formula
Subtract twice the wall thickness from the outer diameter to get the inner (bore) diameter. Halve that for the inner radius, convert it to metres, then apply V = πr²h using the pipe length as h. Multiplying the result in cubic metres by 1,000 converts it to litres.
| Term | Meaning |
|---|---|
| V | Internal volume the pipe can hold, in cubic metres or litres. |
| Outer diameter | The diameter across the outside of the pipe, as it is normally specified or sold. |
| Wall thickness | The thickness of the pipe material itself, subtracted twice (once from each side) to reach the bore. |
| Inner diameter | The bore diameter, equal to outer diameter minus twice the wall thickness. |
The inputs explained
| Field | What to enter |
|---|---|
| Outer diameter (mm) | The outer diameter of the pipe, as printed on the pipe or its packaging. |
| Wall thickness (mm) | The wall thickness of the pipe. Use 0 if you already know the true inner (bore) diameter and want to enter it directly as the outer diameter. |
| Pipe length (m) | The length of pipe being filled. |
When to use it
Working out how much water a length of pipe holds
Before filling, draining or dosing a chemical into a pipe run, knowing its exact internal volume in litres avoids under- or over-estimating how much liquid is involved.
Sizing a header tank or buffer volume
Some heating and irrigation systems use a length of larger-diameter pipe as a simple buffer tank; working out its litre capacity from diameter and length sizes that buffer correctly.
Comparing pipe sizes for a given run length
For a fixed length, capacity grows with the square of the inner diameter, so stepping up even one nominal pipe size can noticeably change how much a run holds.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How capacity changes with outer diameter at a fixed 5 mm wall and 10 m length
A fixed 5 mm wall thickness and 10 metre length, across a range of outer diameters.
| Outer diameter | Capacity | Inner diameter |
|---|---|---|
| 50 mm | 12.57 L | 40.00 mm |
| 80 mm | 38.48 L | 70.00 mm |
| 100 mm | 63.62 L | 90.00 mm |
| 150 mm | 153.94 L | 140.00 mm |
| 200 mm | 283.53 L | 190.00 mm |
| 300 mm | 660.52 L | 290.00 mm |
Questions
Why does the calculator ask for outer diameter and wall thickness instead of just the inner diameter?
Pipes are almost always sold and labelled by outer diameter, with wall thickness given separately as a schedule or pressure rating. Working from those two figures, the ones actually printed on the pipe, avoids needing to measure the bore directly.
What if I already know the exact inner diameter?
Enter it as the outer diameter and set wall thickness to 0. The calculator then treats the entered diameter as the bore itself.
Does wall thickness affect how much the pipe can hold?
Yes, directly. A thicker wall reduces the bore for the same outer diameter, and because volume depends on the square of the radius, even a modest change in wall thickness has a noticeable effect on capacity, especially for smaller-diameter pipes.
How is this different from a general cylinder volume calculator?
A generic cylinder volume tool works from a single radius or diameter, which is fine when you already know the bore. This calculator is built around how pipes are actually specified, outer diameter and wall thickness, and reports the result in litres, the unit most pipe-capacity questions are really asking about.
For a generic cylinder without the pipe-specific outer diameter and wall thickness framing, see the volume of a cylinder calculator.