There’s a widely used rough starting point, and then there’s your actual room — the two aren’t always the same number.
The starting formula
A commonly cited baseline is roughly 100 W of cooling per square meter in a standard, reasonably insulated room. Dreo’s own guidance for the AC318S is more generous, at roughly 210 W per m² — useful context for how much manufacturer guidance itself can vary.
What pushes the number higher
A south- or west-facing room with large windows, a top-floor flat under an uninsulated roof, or a room that regularly holds several people all need more capacity than the base formula suggests. Our full sizing guide covers each factor in more depth.
Fixed m² ratings assume a standard ceiling
Temprium rates the YPK11S at up to 20 m (66 ft)² with no stated ceiling height. A room with a 3 m (10 ft) ceiling holds notably more air than one at 2.4 m (8 ft) for the same floor area — volume, not floor area, is what the compressor actually works against.
What we would not do
Treat any single BTU-per-m² formula as precise for every room. It’s a starting estimate — adjust up for sun, insulation and ceiling height rather than trusting the number in isolation.
The questions that keep coming up
Is it fine to round up to the next BTU tier if I am unsure?
Generally yes, within reason — a slightly oversized unit is usually a safer error than an undersized one, though very oversized units can cool too fast to also dehumidify a room properly. See our guide to sizing an air conditioner for the full reasoning.
Last reviewed 24 August 2026