How much a pipe holds
Pipe volume is the fluid a run of pipe contains, set by its inside diameter and length. It is the number you need to size a fill, estimate a flush, dose a system, or work out how heavy a line gets when full. This calculator takes the outside diameter and wall thickness, finds the bore, and returns both the volume and the practical capacity in gallons or litres.
The formula
Inside diameter = outside diameter minus twice the wall thickness. Internal volume = pi x (ID / 2) squared x length. Capacity in US gallons is the volume in cubic inches divided by 231; in metric, cubic millimetres divided by one million gives litres.
Why wall thickness matters
Two pipes with the same outside diameter can hold very different amounts. A schedule 80 pipe has thicker walls and a smaller bore than schedule 40 of the same nominal size, so it holds less. Always work from the actual wall thickness, not the nominal size.
Full-of-water weight
The calculator also gives the weight of water filling the pipe, at 8.34 lb per US gallon or 1 kg per litre. Add that to the pipe metal weight when checking hanger spacing and support loads on long horizontal runs.
Where this fits
For the weight of the pipe itself, use the pipe weight calculator; for coating or paint area, the pipe surface area calculator.
Worked example
A 4 in pipe with a 0.237 in wall and 10 ft long has a bore of 3.526 in. Its volume is about 1172 cubic inches, or roughly 5.07 gallons, weighing about 42 lb when full of water.
FAQ
Do I use inside or outside diameter?
Capacity uses the inside diameter. Enter the outside diameter and wall thickness and the calculator finds the bore for you.
Does length unit have to match diameter unit?
Here diameters are in inches or millimetres while length is in feet or metres — the calculator handles the conversion, so enter each in the unit shown.