Pipe Volume Calculator

To calculate the internal volume of any cylindrical pipe, use the cylinder volume formula: V = π × r² × L, where r is the pipe inside radius (Inside Diameter / 2) and L is the length of the pipe. Ensure radius and length are in matching units before calculating.

To convert internal pipe volume to US liquid gallons, divide the volume in cubic inches by 231 (since 1 US gallon = 231 cubic inches): Gallons = (π × r² × L) / 231. For example, a 2-inch ID pipe that is 100 feet long holds approximately 16.32 US gallons.

Always use the actual inside diameter (ID) for true hydraulic capacity calculations. Nominal Pipe Size (NPS) is only an industry classification. Schedule 40, Schedule 80, and Copper Type K, L, and M pipes of the same nominal size have different internal diameters due to varying wall thicknesses.

Multiply the total volume in US gallons by 8.34 lbs (the weight of 1 US gallon of fresh water at 62°F / 16.7°C). If calculating in metric units, 1 Litre of water weighs exactly 1 kilogram (2.205 lbs).

For metric measurements (millimeters and meters), calculate internal volume in cubic meters: V (m³) = π × (ID in mm / 2000)² × (Length in meters). Multiply cubic meters by 1,000 to get the exact liquid capacity in Litres.

In a fully pressurized closed piping system (such as domestic potable water or hydronic heating), pipe slope does not affect internal fluid capacity. However, in open gravity drainage systems (DWV), sloped pipes generally run partially full (1/3 to 1/2 depth) to allow airflow and sewer gas venting.