What formula does this calculator use?

It uses Q = A x v, where Q is volumetric flow rate, A is the circular cross-sectional area (pi * r^2), and v is the average fluid velocity. This is the standard continuity equation for incompressible, steady-state flow.

What is the difference between inner diameter and outer diameter?

Inner diameter (ID) is the internal bore through which fluid flows. Outer diameter (OD) includes the pipe wall thickness. Always use inner diameter for flow calculations because that is the actual flow passage area.

What units are supported?

You can enter diameter in millimeters (mm) or inches (in), and velocity in meters per second (m/s) or feet per second (ft/s). Results are shown in m3/s, L/s, US GPM, and CFM.

Does this calculator account for friction losses?

No. This calculator computes theoretical flow rate based on geometry and velocity alone. Real-world flow is reduced by friction, fittings, and elevation changes. Use the Darcy-Weisbach or Hazen-Williams equations for head-loss analysis.

What is a typical water velocity in pipes?

For domestic water supply, 0.6–2.4 m/s (2–8 ft/s) is typical. Velocities above 3 m/s can cause noise, erosion, and water hammer. Drainage pipes often run partially full at lower velocities.

Pipe Flow Rate Calculator

Enter pipe inner diameter and fluid velocity to instantly calculate volumetric flow rate using Q = A x v.

Pipe Parameters

Inner Diameter

Fluid Velocity

Flow Rate Results

Enter diameter and velocity, then click Calculate.

Typical Pipe Velocities

Application	Velocity (m/s)	Velocity (ft/s)
Domestic cold water supply	0.6 – 2.0	2 – 6.6
Hot water supply	0.5 – 1.5	1.6 – 5
Irrigation main line	0.6 – 1.5	2 – 5
HVAC chilled water	1.0 – 2.4	3.3 – 8
Fire suppression	1.5 – 3.0	5 – 10

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Summary

This tool calculates the volumetric flow rate (Q) of fluid through a circular pipe using the formula Q = A x v, where A is the cross-sectional area of the pipe and v is the average fluid velocity. Results are shown in cubic meters per second, liters per second, US gallons per minute, and cubic feet per minute. It is useful for plumbing design, HVAC ducting, irrigation systems, and any piped fluid conveyance project.

How it works

Enter the pipe inner diameter in millimeters or inches.
Enter the average fluid velocity in meters per second or feet per second.
The calculator computes the cross-sectional area: A = pi * (d/2)^2.
Flow rate Q is derived from Q = A x v.
Results are displayed in m3/s, L/s, GPM, and CFM simultaneously.
Adjust either input to instantly recalculate.

Use cases

Size water supply pipes for residential or commercial plumbing.
Calculate flow rates for irrigation and sprinkler systems.
Verify HVAC duct airflow capacity.
Design drainage and stormwater systems.
Check pump output against required flow rates.
Estimate fire suppression water demand.
Validate pipe sizing for industrial process pipelines.
Convert flow rates between metric and imperial units.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu