How much wider than my window should the curtains be?

The standard guideline is 1.5 to 2 times the window width for proper fullness and edge coverage. So a 60 inch window should get about 90 120 inches of total curtain width (one 45 inch panel on each side, or two 60 inch panels). For serious blackout, go wider so the panels can overlap in the center and wrap around the edges.