How Do You Choose the Right Curtain Width for Your Windows?

Spent way too long on this for my living room before someone told me curtain width isn't about the window at all, it's about the rod. Rule of thumb is roughly double the rod width in fabric, a bit less for heavy stuff like velvet, a bit more for light sheers. My first set of window curtains were cut to the glass width and looked flat and stretched, almost like a bedsheet. Extending the rod several inches past the frame on each side also helped, since the open curtains stack on the wall and stop blocking daylight. Got the measuring done at home by Kingdom of Curtains since they do free doorstep measurement across Delhi NCR. Anyone else make the "match the window" mistake?