The answer to 'what size recessed lighting do I need' is that the size of recessed lighting you need depends on the size of the room, the ceiling height, and the desired light output. As a general guideline, you'll want to use 4-inch recessed lights for smaller rooms with 8-foot ceilings, 5- or 6-inch lights for medium-sized rooms with 9-foot ceilings, and 6-inch or larger lights for larger rooms with higher ceilings. The wattage of the bulbs you use will also impact the overall light output.
When choosing recessed lights, it's important to consider factors like the room's dimensions, ceiling height, and the desired brightness and ambiance. You'll also want to make sure the lights are properly spaced to provide even, adequate lighting throughout the space. If you're unsure of the right size or configuration, it's best to consult with a professional electrician who can assess your specific needs and make recommendations.