Ductwork Size Calculator

Introduction: The Ductwork Size Calculator is a tool designed to help determine the required size of ductwork for a ventilation system. Properly sized ducts are essential for efficient airflow and HVAC system performance. This calculator considers the airflow rate and air velocity to provide users with the recommended ductwork size in square inches.

Formula: The calculator utilizes the airflow rate (in cubic feet per minute – CFM) and air velocity (in feet per minute – FPM) to calculate the ductwork size. The formula involves dividing the airflow rate by the air velocity to determine the cross-sectional area of the ductwork.

How to Use:

  1. Enter the airflow rate in CFM.
  2. Enter the air velocity in FPM.
  3. Click the “Calculate” button to obtain the recommended ductwork size in square inches.

Example: For example, if the airflow rate is 400 CFM and the air velocity is 800 FPM, the calculator will determine and display the recommended ductwork size.


  1. Q: Why is ductwork sizing important? A: Properly sized ductwork ensures optimal airflow, energy efficiency, and system performance in HVAC installations.
  2. Q: What happens if ductwork is undersized? A: Undersized ducts can lead to reduced airflow, increased energy consumption, and inadequate heating or cooling in the target space.
  3. Q: Can I use the Ductwork Size Calculator for residential HVAC systems? A: Yes, the calculator is suitable for both residential and commercial applications.
  4. Q: Are there industry standards for ductwork sizing? A: Yes, industry standards and guidelines are available, and HVAC professionals often follow them for accurate duct sizing.
  5. Q: How can I measure air velocity in a duct? A: Air velocity can be measured using an anemometer, a device designed to measure the speed of airflow.

Conclusion: The Ductwork Size Calculator provides a straightforward solution for determining the recommended duct size based on airflow rate and air velocity. Accurate duct sizing is crucial for achieving optimal HVAC system performance and maintaining comfortable indoor environments. Users are encouraged to adhere to industry standards and seek professional advice for complex HVAC projects.

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