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)

Results

Liters — L

US Gallons — gal

Cubic Meters — m³

Cubic Inches — in³

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Summary

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

How it works

Select your preferred unit system — metric (mm/cm/m) or imperial (in/ft).
Enter the inner diameter of the pipe.
Enter the total length of the pipe.
The volume is calculated instantly using the formula V = π × (d/2)² × L.
Results appear in liters, US gallons, cubic meters, and cubic inches.
Click any result to copy it to your clipboard.

Use cases

Calculating how much water a plumbing pipe holds for pressure testing.
Estimating fluid volume in irrigation or sprinkler system pipelines.
Sizing expansion tanks and buffer tanks for HVAC systems.
Determining fill times when flooding or draining pipe sections.
Comparing pipe capacities when choosing between different pipe diameters.
Calculating chemical or coolant volume in industrial process piping.
Estimating weight of fluid-filled pipes for structural load calculations.
Teaching pipe flow and hydraulics concepts in engineering courses.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu