Free HVAC Duct Sizing Calculator for Contractors
Go beyond basic sizing. Engineer a perfectly balanced duct system that guarantees optimal airflow, peak efficiency, and client satisfaction on every project.
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How to Calculate Duct Size with Our Tool
Get the dimensions you need in three simple steps:
Enter Airflow (CFM)
Input total cubic feet per minute required for the space or duct run.
Set Friction Loss Rate
Enter your target friction loss rate (e.g., 0.1 in WG/100 ft).
Get Instant Dimensions
The calculator provides ideal round and equivalent rectangular duct sizes.
Your Calculation is Done. Now, Let's Build the Project.
Once your calculation is complete, connect it to Duct Architect's platform for quotes, inventory, and field management.
- Instant quotes based on your calculations
- Real-time inventory tracking
- Streamlined field management tools
- Integrated project documentation
Why Accurate Duct Sizing Matters for Contractors
Preventing Callbacks
Correct sizing eliminates noisy airflow and hot/cold spots, ensuring your clients are satisfied from day one and reducing costly return visits.
Protecting Equipment
Reduces strain on fan motors and components for a longer system lifespan, minimizing maintenance costs and equipment failures.
Boosting Your Reputation
Deliver energy-efficient systems that perform as promised, building trust and generating referrals for future projects.
Frequently Asked Questions
Quick answers to questions you may have about Free Calculator
What is a Duct Size Calculator?
A Duct Size Calculator is an essential tool used by HVAC contractors and engineers to determine the optimal dimensions for a system's ductwork. Based on key inputs like airflow (CFM) and friction loss, it calculates the required size for both round and rectangular ducts to ensure balanced airflow, peak system performance, and maximum energy efficiency.
How do you calculate air duct size?
The most common method for calculating air duct size involves balancing two key factors: Airflow (CFM) and Friction Loss. Airflow represents the volume of air needed for the space, while Friction Loss is the acceptable pressure drop that ensures air moves efficiently without being too noisy or slow. An HVAC duct sizing calculator automates this complex calculation; by simply entering these two values, the tool instantly provides the optimal round and equivalent rectangular duct dimensions required for a balanced and efficient system.
The most common method for calculating air duct size involves balancing two key factors: Airflow (CFM) and Friction Loss. Airflow represents the volume of air needed for the space, while Friction Loss is the acceptable pressure drop that ensures air moves efficiently without being too noisy or slow. An HVAC duct sizing calculator automates this complex calculation; by simply entering these two values, the tool instantly provides the optimal round and equivalent rectangular duct dimensions required for a balanced and efficient system.
What is the best friction loss rate for duct sizing?
For most residential and light commercial HVAC systems in the US, a friction loss rate of 0.1 in. WG per 100 feet is the industry standard for main trunk ducts. For smaller branch runs, a rate closer to 0.08 in. WG is common. Our calculator gives you the flexibility to input the precise rate your project requires.
For most residential and light commercial HVAC systems in the US, a friction loss rate of 0.1 in. WG per 100 feet is the industry standard for main trunk ducts. For smaller branch runs, a rate closer to 0.08 in. WG is common. Our calculator gives you the flexibility to input the precise rate your project requires.
How does this calculator handle rectangular vs. round ducts?
Our calculator first determines the ideal round duct diameter for optimal airflow efficiency. It then instantly provides a list of equivalent rectangular duct dimensions (with different width-to-height ratios) that deliver the same performance, giving you the flexibility to adapt to real-world structural constraints on the job site.
Our calculator first determines the ideal round duct diameter for optimal airflow efficiency. It then instantly provides a list of equivalent rectangular duct dimensions (with different width-to-height ratios) that deliver the same performance, giving you the flexibility to adapt to real-world structural constraints on the job site.