What size humidifier do I need for my bedroom?

For a standard bedroom (150 300 sq ft), a humidifier with a 1 1.5 gallon tank runs through the night without refilling. For larger master bedrooms (300 500 sq ft), look for 1.5 2 gallon tanks. Tank size directly correlates with runtime a 1 gallon tank at medium output lasts roughly 10 12 hours. Oversizing slightly is fine (the humidifier adjusts output), but a drastically oversized unit wastes energy and counter space.