Duct Calculator: Find the Right Duct Size by CFM or Tonnage Duct Calculator: Size Any Supply or Return Duct in Under a Minute Get the right round or rectangular duct size from CFM, AC tonnage, or room area. Built on the same ASHRAE friction chart method HVAC pros use with a ductulator, with velocity checks … Continue reading Duct Calculator: Find the Right Duct Size by CFM or Tonnage