What size humidifier do I need?

How humidifier sizing works

Humidifiers are rated by how much moisture they add per day (gallons/day) and the area they cover. A rough guide is about one gallon per day for every ~350 sq ft in moderately dry air — more in winter or very dry climates. Too small and it can’t keep up; too large and you risk over-humidifying (aim for 30–50% indoor humidity). Evaporative and ultrasonic units run quietest; warm-mist adds a little heat.