What is the governing ratio for thin walled cylinders?

D/t>20

Explanation:

Lets take

D = Diameter of thin cylinder

t = Thickness of thin cylinder

So a cylinder is called thin cylinder if the ratio of diameter to the thickness is greater than 20 (D/t>20).

But on the other hand a cylinder is called thick cylinder is ratio of thickness to the diameter is greater than 20 (t/D>20).

So the governing ratio of thin walled cylinder is 20.