SEAGULL.MY ONLINE DUCT SIZING CALCULATOR
Use this Smart Ductalator to Manual filled in your Design Value and Work Out a Reommended Duct Size
*Calculations based on ASHRAE Darcy-Weisbach / Huebscher formulas. Accuracy is aligned with standard HVAC slide rules.
RECOMMEND DUCT VELOCITY (FPM)
To ensure the Seagull Smart Ductulator provides the most professional guidance for your customers, it is essential to follow industry-standard velocity limits. If air moves too fast, it creates noise and vibration; if it moves too slow, it fails to distribute cool air effectively.
Below is a comprehensive table of recommended and maximum duct velocities based on ASHRAE and SMACNA standards, tailored for various building types.
Recommended & Maximum Duct Velocities (FPM)
| Building Type | Designation | Recommended Velocity (FPM) | Maximum Velocity (FPM) |
| Residences | Main Ducts | 700 – 900 | 1,000 |
| Branch Ducts | 600 | 800 | |
| Branch Risers | 500 | 700 | |
| Theaters / Auditoriums | Main Ducts | 800 – 1,000 | 1,200 |
| Branch Ducts | 600 | 800 | |
| Branch Risers | 500 | 700 | |
| Schools / Offices | Main Ducts | 1,000 – 1,300 | 1,500 |
| Branch Ducts | 800 | 1,000 | |
| Branch Risers | 600 | 800 | |
| Public Buildings | Main Ducts | 1,200 – 1,500 | 1,800 |
| Branch Ducts | 1,000 | 1,200 | |
| Branch Risers | 800 | 1,000 | |
| Industrial Buildings | Main Ducts | 1,500 – 2,200 | 2,500+ |
| Branch Ducts | 1,200 | 1,600 | |
| Branch Risers | 1,000 | 1,200 |
Material Selection (TO AWARE)
Why Material Selection is Crucial:
In Malaysia, many residential AC installations use Flexible Ducting (those shiny silver tubes). A common mistake is using the same size for Flex as you would for Rigid Metal. Because Flex ducting has a corrugated internal surface, it creates "Micro-Turbulence" which slows air down.
How to use this for your project:
-
Galvanized Steel: Best for commercial projects and shop lots with exposed ceilings.
-
Flexible Duct: Use this for residential attic/plenum work.
-
Note: If the flex duct is not pulled tight, the friction loss can double, and this need to be aware to help engineers account for that real-world error.
CONVERSION TABLE
Pressure Units Conversion Table
This table shows the equivalent value of 1 unit of the source (left column) converted into the target units (top row).
| From ↓ / To → | PSI | kg/cm2 | In. W.g. | Ft. W.g. | Pascal (Pa) |
| 1 PSI | 1 | 0.0703 | 27.71 | 2.309 | 6,894.7 |
| 1 $kg/cm^2$ | 14.223 | 1 | 393.7 | 32.81 | 98,066.5 |
| 1 In. W.g. | 0.0361 | 0.0025 | 1 | 0.0833 | 249.09 |
| 1 Ft. W.g. | 0.4335 | 0.0305 | 12 | 1 | 2,989.1 |
| 1 Pascal (Pa) | 0.000145 | 0.00001 | 0.0040 | 0.0003 | 1 |
Flowrate Units Conversion Table
This table shows the equivalent value of 1 unit of the source (left column) converted into the target units (top row).
| From ↓ / To → | L/s | m3/hr (CMH) | m3/s | U.S. G.P.M. | CFM |
| 1 L/s | 1 | 3.6 | 0.001 | 15.85 | 2.119 |
| 1 $m^3/hr$ (CMH) | 0.2778 | 1 | 0.000278 | 4.403 | 0.5886 |
| 1 $m^3/s$ | 1000 | 3600 | 1 | 15,850 | 2,118.9 |
| 1 U.S. G.P.M. | 0.0631 | 0.2271 | 0.000063 | 1 | 0.1337 |
| 1 CFM | 0.4719 | 1.699 | 0.000472 | 7.481 | 1 |
OPTIONAL DUCTALATOR
This free, easy-to-use ductulator helps you quickly calculate duct velocity and pressure drop based on design airflow — no charts, no guesswork, and no physical duct wheel required.
A. Calculate with cfm & friction loss
1.Enter Design CFM & Friction Loss
2.This Ductalator base on air pressure drop per 100 ft
Pro Duct Sizing Tool
Multi-Shape Airflow Calculator
Recommended Duct Sizes
B. Calculate with cfm & DUCT DIAMETER
1.Enter Design CFM
2.Adjust duct size by clicking Up or Down
Interactive Ductulator
Adjust Size or Flow to see Performance