Duct Sizer Calculator
Calculate optimal duct sizes using Equal Friction or Equal Velocity methods. Supports round and rectangular ducts with pressure drop analysis based on McQuay methodology.
Switch between Imperial and Metric
Cubic Feet per Minute (CFM)
Enter duct run length to calculate total pressure drop
Round Duct
14"
Rectangular Equivalent
18" × 9"
Actual Velocity
935 FPM
Dimensions
25 × 0 in
Equivalent Diameter
13.7 in
Aspect Ratio (W:H)
1:2.00
DISCLAIMER
This calculator provides ESTIMATES for preliminary planning purposes. Results are based on standard assumptions and may not reflect your specific project conditions.
By using this tool, you acknowledge that:
1. All calculations are approximate and based on typical industry standards and assumptions.
About This Calculator
The Duct Sizer Calculator helps MEP engineers and HVAC contractors determine optimal ductwork dimensions for air distribution systems across the UAE and Gulf. Size round and rectangular ducts using Equal Friction or Equal Velocity methods based on ASHRAE and McQuay methodologies. Essential for achieving balanced airflow, minimizing pressure drop, and ensuring quiet operation in commercial and residential buildings.
When to Use This Calculator
- Designing HVAC ductwork for new buildings
- Sizing supply and return air ducts
- Checking velocity limits for noise control
- Calculating pressure drop for fan selection
- Converting between round and rectangular duct equivalents
How to Use This Calculator
Enter Airflow Rate
Input the required airflow in CFM (cubic feet per minute) or L/s for the duct section.
Select Sizing Method
Choose Equal Friction (constant pressure drop/length) or Equal Velocity method.
Set Design Parameters
Specify maximum velocity (typically 6-10 m/s for mains) or friction rate (0.8-1.2 Pa/m).
Choose Duct Shape
Select round or rectangular duct, with aspect ratio limits for rectangular.
Review Results
Get recommended duct size, velocity, pressure drop, and equivalent diameter.
Typical Scenarios in UAE & Gulf Projects
A 30-story office tower needs main supply duct sizing for 20,000 CFM from the AHU. Using Equal Friction method at 0.1" WG per 100ft, the calculator recommends 36" diameter round duct or equivalent 40"×24" rectangular at 1,100 fpm velocity, staying below noise criteria for office spaces.
A food court requires kitchen exhaust duct sizing for 8,000 CFM with grease-laden air. The calculator sizes a 24" round duct at 2,000 fpm (above minimum grease velocity) with 0.15" friction rate for the high-velocity grease duct requirements.
Frequently Asked Questions
Take Your Calculations Further
This calculator reflects the logic built into Arkan's construction management platform.
Last Updated: January 2026
Standards Reference: Calculations based on ASHRAE Handbook of Fundamentals and SMACNA standards