These handy devices/programs allow you to calculate Areas, Velocities, Flowrates, Pressure Losses and a load more design criteria either using a simple hand held circular slide rule type device …. or more recently apps for your Android or Apple device.

I have not personally tested the latter and would welcome feedback on anyone who has.  Some of the web feedbacks on these are not good – but the ones selected below appear to have reasonable feedback.

Android Apps (2021 prices)

Apple App


For the manually operated (well known) circular Trane Ductulator – you will need to search eBay.  It will probably be eBay USA (where I bought mine) but even with shipping the total cost was around £16.