Room size calculator: what area will this unit handle?
FreezAir is reader-supported. When you buy through links on our site, we may earn a commission at no extra cost to you. This never influences our scores. How we make money.
This room size calculator runs the sizing math backwards: give it a unit’s cooling capacity and it returns the area that unit can honestly handle — plus a no-nonsense mode for evaporative devices, which have no honest square-footage at all.
Compressor math: area ≈ DOE BTU ÷ 20 BTU/ft², shown with a comfort band (÷25 for sunny/poorly insulated, ÷16 for shaded/modern). Evaporative devices return an effective personal zone, not an area — that is the honest unit for the class.
Why the two modes exist
A compressor rating maps to area because refrigeration capacity is fixed; divide the DOE BTU by the 20 BTU/ft² baseline and you have the realistic room, give or take conditions. An evaporative cooler’s output floats with humidity and its benefit is directional — the truthful answer is “a zone roughly 1–2 metres in front of the outlet”, which is what our second mode says instead of inventing square feet.
Next step
Have a room and need the unit instead? Use the forward BTU calculator. Shopping the small end? The under-$300 guide splits the compressor and personal lanes honestly.
Frequently asked questions
How does the room size calculator convert BTU to area?
It inverts the sizing baseline: area ≈ DOE BTU ÷ 20 per square foot, with a shown ± band for insulation and sun. Enter the DOE (SACC) figure, not ASHRAE — the bigger label number overstates portables by 20–40%.
Why is there an evaporative mode?
Because evaporative and personal coolers have no honest BTU-to-area mapping — their effect is a directional zone, not room coverage. The mode answers in metres of effective reach instead of pretending square footage.
The box says 1,300 sq ft — is that real?
For low-watt evaporative devices, no: that is airflow-reach marketing, not temperature control. Our 45 W analysis shows exactly why, with the arithmetic.
What if my room is between sizes?
Round the requirement up half a step for sunny or busy rooms, down for shaded and empty ones — then verify with the full BTU calculator, which handles the adjustments properly.