Duct Diameter Tape Measure
This crafty little device is a breeze to use 🙂
Simply wrap the (very) thin retractable tape measure around the duct and read of the duct Diameter!! So clever and so easy.
Obviously the tape scale simply converts Circumference using the equation ΠD to get the diameter.
Not the most robust/heavy duty manufacture but it is inexpensive and should last for some time.