Duct size calculator
Use our duct size calculator to calculate accurate size and measurement values instantly.
Calculator
Estimate circular duct diameter from airflow and target air velocity.
Formula: Area(ft^2) = CFM / velocity(fpm), diameter from A = pi x d^2 / 4
What each field means
- Airflow (CFM): Enter a valid value for this field.
- Target Velocity (fpm): Example: 800
Estimated Duct Diameter (in)
Your result will appear here.
About Duct size calculator
The Duct size calculator helps you estimate AC and HVAC values quickly using consistent assumptions and practical calculation rules.
Formula Explanation
Area(ft^2) = CFM / velocity(fpm), diameter from A = pi x d^2 / 4
Inputs You Need
- Required measurement values relevant to this calculator
- Unit selection: Airflow (CFM), Target Velocity (fpm)
- Optional tolerance, safety, or scenario values if applicable
Step-by-Step Usage
- Enter your known values in the calculator fields.
- Select units and options that match your scenario.
- Click Calculate to generate your output.
- Copy, save, or share the result for later reference.
Example
Run the tool with realistic values from your use case and compare the output against expected ranges for AC and HVAC calculations.
Frequently Asked Questions
Is this Duct size calculator accurate?
Yes, when correct inputs and units are provided.
Which units does this calculator support?
This tool is optimized for Airflow (CFM), Target Velocity (fpm).
Can I use this calculator on mobile?
Yes, the form is optimized for touch inputs and smaller screens.