864 square feet. 9-1/2' ceiling. Two experts who are familiar with the local climate tell me 12,000 will do ... I'll take their advice !! Humidity is a big issue so the near continuous operation should help resolve that. This is Canada - you don't get a 12,000 BTU mini-split for $1000 !!! Lowes was just under $2000 for a "Mr Cool" but the unit I'm getting is top of the line and because they're installing it has a one year parts and labour warranty and a ten year parts warranty. Anyhow, its a done deal.