To calculate the profile and the outside dimension of a cone from a flat plate. A cone for a column for example is usually first cut out a flat plate and then rolled to shape.
A design calculation has to be done to determine the actual dimensions of the strike-out from the flat plate. Some extra margins (allowances) can be added to the ends of the cone to be able to prepare the ends (for example by grinding) for welding purposes. Below figure indicates the meaning of the required dimensions necessary to execute the design calculation.