What diameter should I use — inner or outer?

Always use the inner diameter (ID) for volume calculations. The inner diameter is the clear opening inside the pipe wall. For common pipe standards, the inner diameter is smaller than the nominal size printed on the label.

How is pipe volume calculated?

The formula is V = π × r² × L, where r is the inner radius (inner diameter ÷ 2) and L is the pipe length. This gives cubic units that the calculator automatically converts to liters, gallons, and cubic meters.

What is the difference between inner diameter and nominal diameter?

Nominal diameter (NPS, DN) is a label used for reference — it rarely matches the actual inner diameter. Always measure the actual inner bore, or look up the schedule-specific ID in a pipe data table for your pipe standard (e.g. Schedule 40, Schedule 80).

How do I convert the result to kilograms of water?

Water has a density of approximately 1 kg per liter at room temperature. So the volume in liters equals the weight in kilograms. For other fluids, multiply the liter result by the fluid's specific gravity.

Does this work for non-circular pipes?

No. This calculator assumes a perfect cylinder. For oval, rectangular, or other cross-sections, you would need to calculate the cross-sectional area separately and multiply by the length.

How many liters are in a US gallon?

One US gallon equals approximately 3.78541 liters. The calculator uses this exact conversion factor for all gallon results.

Pipe Volume Calculator

Name: Pipe Volume Calculator
Availability: InStock
Author: Nham Vu

Calculate the internal volume of a cylindrical pipe from its inner diameter and length, with results in liters, US gallons, and cubic meters.

Unit System

Pipe Dimensions

Inner Diameter (mm)

Pipe Length (m)

Enter the pipe diameter and length on the left to get the volume

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Summary