Pipe Diameter (mm) Enter the inside diameter of the round pipe in millimeters (e.g., 150)

Air Velocity (m/s) Enter the average air speed inside the pipe in meters per second (e.g., 8)

Quick Examples:

Small Ventilation Duct Industrial Compressed Air Pipe

Calculate Clear

This calculator is for informational purposes only. Verify results with appropriate professionals for important decisions.

Enter your pipe diameter in millimeters and air velocity in meters per second, then click Calculate to view your air flow rate in cubic meters per hour. Use the Quick Examples buttons to try common duct sizes for homes, offices, and factories.

What Is Air Flow Rate Through Pipe

Air Flow Rate Through Pipe is the volume of air that moves through a round pipe in a set amount of time. It is found by multiplying the open space inside the pipe by how fast the air is traveling. This number tells you how much air a duct or pipe can deliver. Engineers use it to pick the right pipe size for ventilation, cooling, and compressed air systems so the air reaches where it is needed.

How Air Flow Rate Through Pipe Is Calculated

Formula

First, the pipe diameter in millimeters is changed to meters by dividing by 1000. Then the inside open space of the pipe is found using the circle area formula, which is pi times the diameter squared, divided by four. This gives the cross-sectional area in square meters. Next, that area is multiplied by the air velocity in meters per second to get the flow rate in cubic meters per second. Finally, the answer is multiplied by 3600 to change it into cubic meters per hour, which is the unit most often used for airflow in India.

Why Air Flow Rate Through Pipe Matters

Knowing the air flow rate helps you pick a pipe that delivers the right amount of air without wasting energy. A pipe that is too small restricts flow, while a pipe that is too large costs more than needed. This number guides smart design choices for homes, offices, and factories.

Why Correct Pipe Sizing Is Important for Air Systems

When a pipe is undersized, air speeds up and pressure drops, which can starve equipment of the air it needs and raise power bills. Oversized pipes cost more upfront and waste valuable space. Wrong sizing can also cause noisy flow, vibration, or uneven cooling across rooms. Getting the flow rate right helps avoid these problems and keeps the system running smoothly for years with lower running costs.

For HVAC Ventilation

In ventilation work, the flow rate sets how much fresh air reaches each room. Designers aim for target air changes per hour, so they use this calculator to choose duct sizes that meet those targets. A typical office duct may run between 5 and 10 meters per second to balance comfort, noise, and energy use.

For Industrial Compressed Air

Compressed air lines often use higher velocities, but too much speed causes large pressure loss. Plant engineers use this calculator to keep velocity within recommended limits, usually below 20 meters per second for main lines. This protects tools at the far end of the pipe from losing power. Smaller branch lines may run a bit slower to avoid extra friction.

Air Flow Rate vs Mass Flow Rate

Air Flow Rate measures volume, such as cubic meters per hour. Mass Flow Rate measures weight, such as kilograms per hour. Two pipes with the same volumetric flow can move different masses of air if temperature or pressure differs. For most duct sizing, volumetric flow is enough, but compressors and dryers often need mass flow instead.

For Advanced Users

At very high velocities or pressures, air no longer behaves like a simple fluid. Compressibility, friction, and temperature changes start to matter, and the basic formula gives only an estimate. Advanced users may apply correction factors or use specialized software for long pipelines, high-pressure compressed air systems, or large industrial plants where small errors add up quickly.