There is another way to figure this.
Start by deciding on your print size. Put something that size as a sample where the print will be hung.
With your camera stand where it will normally be viewed from. Zoom or switch lenses until the sample is tightly framed.
Use the focal length you find to shoot the portrait. This gives the viewer the same view as the camera.
Wide angle shots only look distorted when viewed from to far away or put another way printed too small for the intended viewing distance.