Yes it is possible, but unless the hole happens to be a standard size and shape, it won't be so easy. The ASHRAE handbook has a lot of information on "duct pressure drop" including a formula for this very thing. What size and shape of hole do you have, and do you have an idea what CFM or pressure drop you are expecting? Are you trying to control airflow? -- Lawrence Lile John Pearson Sent by: pic microcontroller discussion list 10/01/02 10:03 AM Please respond to pic microcontroller discussion list To: PICLIST@MITVMA.MIT.EDU cc: Subject: CFM calc. from pressure drop? Is it possible to determine, or even estimate, the CFM passing through a hole by reading the pressure difference on each side of the hole. This would be ambient air at average humidity and about 75 degrees F. Thanks John -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.