What size subwoofer do I need for my room?

Reddit consensus on r/BudgetAudiophile and r/hometheater suggests 10-inch subs like the Klipsch R-100SW or Polk PSW10 are typically enough for rooms under ~200 sq ft, while 12-inch models (Klipsch R-12SW, SVS SB-1000 Pro) are recommended for medium-to-large living rooms. Multiple users specifically flag that the SVS SB-1000 Pro can run out of headroom in very large rooms used for movies.