You don't.
Perimeter is a concept associated with plane figures, not solid shapes.
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The shape described cannot be a cone since a cone has a base at one end and a point - of zero length - at the other!
With great difficulty because a cone is a 3D object and only 2D shapes have perimeters
A person can calculate the volume of a cone by multiplying the height by pi and by the square of the radius of the cone, and then dividing the result of the previous operations by three.
Compute = calculate; perimeter = measurement of the outside edge.
Perimeter of a round plate = 2*pi*radius or pi*diameter