Crown Radius
How to determine the radius for flexible Crown moulding
For "noncrown" applications see: "How to Determine the Radius for NonCrown applications"
There are 3 basic types of radius applications:
Inside Radius (Concave)To calculate the radius of a concave wall you will need to know the width and the depth of the curve. Then use the radius calculator 

Outside Radius (Convex)To calculate the radius of a convex wall:


DormerTo calculate the radius of a dormer you will need to know the width and the rise of the dormer. Then use the radius calculator to calculate the radius. 
The radius does not have to be exact. The moulding will flex to fit as long as the calculated radius is within an inch or 2.