This app is developed to Calculate Duct Size Required with available CFM & FPM. This app calculate Both Rectangular and Round Duct Sizes in Inches. This App is also Calculate Air Flow rate in CFM and this app is also calculate in Air Velocity in FPM. The application is designed for engineers HVAC working in the field of design and installation of ventilation systems. Heating, ventilation, and air conditioning (HVAC) engineers and designers will find this tool to be valuable in their everyday design and construction work