Trying to convert differential pressure (inch WC) measurements from a 6-inch diameter pipe into an air flow rate (cfm). Here's what I got so far... I'm assuming laminar, imcompressible flow with negligible friction, head, or thermal losses (this is a very low-flow system). From the Bernoulli equation... V = (2P/d)^0.5 V = velocity P = differential pressure d = air density @ STP area = A = pi(r^2) flowrate = Q = VA Seems straightforward enough, but when I plug in my pressure readings, I'm getting too high of a result for Q (I get a result I'd expect for a fan, and not the dribbling of air I'm actually getting from the pipe). I think I have the units converted correctly, so am I missing something in the velocity equation?