How to calculate the volume of a pipe
The OmniCalculator pipe volume tool models a pipe as a cylinder and uses the pipe's inner diameter, not the outer diameter. That inner space is the actual liquid-holding capacity of the pipe.
Because radius is half of the inner diameter, the equivalent form is V = π × d² × L / 4. Keep the units consistent before converting the result to liters, cubic feet, or US gallons.
Mass of liquid inside the pipe
Once the internal volume is known, the liquid mass follows directly from density. This is the same relationship highlighted in the Omni reference:
This is useful when checking support loads, startup fill weight, and total system mass in process piping or hydronic loops.
Worked example from the source logic
Using an inner diameter of 15 cm, a length of 6 m, and water at 997 kg/m³, the calculator gives approximately 0.106 m³ of volume and 105.71 kg of liquid mass. That matches the example shown on the fetched OmniCalculator page.