Sorry but that is NOT how it is...
Example325/60R20
325 = section width in mm
60 = aspect ratio (60% of 325 or 195mm of sidewall)
R = radial construction
20 = means you have some blinging 20 inch rims...
You tire would be 20 inches plus 195mm on either side... 195 mm equates to about 15.35 inches...
So your 325/60R20 is about 35 inches tall...
BTW - I have never, never seen a 336 tire! Nor a 325/90...