What size humidifier do I need for a large room or whole house?

Reviewers map tank size to coverage: 2.5–4L units are framed for single bedrooms, 6L models for large rooms running overnight, and 20L-plus evaporative towers for whole-home or open-plan coverage up to roughly 3000 sq ft. Community consensus is that buying a tank far larger than your space invites over-humidification and refill fatigue rather than better results.