https://ductcalc.ca (https://ductcalc.ca)
Just thought sharing this easy to use online Ductulator (Duct Size Calculator) called ductcalc.ca
It works with both I-P (US) and S-I (metric) unit systems. It calculates based on both Static Pressure Loss or Velocity and It generates the dimensions for both duct shapes (round and rectangular).
It works online from any device or browser and it has mobile friendly interface.
It can be accessed easily on the following link. No installation required: https://ductcalc.ca (https://ductcalc.ca)