Room size → BTU, tonnage & unit type
Enter your room size and conditions to get the cooling BTU, tonnage, and unit type you need — plus a furnace estimate for heating. Works in both imperial and metric.
Cooling needed
12,000 BTU
Recommended unit
12,000 BTU
Tonnage
1 ton
Furnace (heating)
25,000 BTU
Best unit type
Window unit or single-zone mini-split
Alternative: Portable AC
Real, widely available units in the Up to 12,000 BTU class. Independent picks — we're not affiliated with any manufacturer or retailer and earn nothing from these links. Always match the unit's BTU to the size above.
Best overall
8,000–12,000 BTU
Window · inverter · U-shape · ~36 dBA · window still opens
The U-shape puts the compressor outside the glass, so it runs about as quiet as a whisper and you can still open the window. Inverter compressor sips power.
Find on AmazonQuietest
8,000–14,000 BTU
Window · dual inverter · Dual-inverter · Wi-Fi · very quiet
LG’s dual-inverter compressor ramps up and down instead of cycling on/off — quieter, steadier temps, and lower running cost than a fixed-speed unit.
Find on AmazonBudget pick
5,000 BTU
Window · fixed-speed · Cheapest way to cool a small room
A no-frills window unit that reliably cools a small bedroom, office, or dorm up to ~150 sq ft for the lowest upfront cost.
Find on AmazonBest value
8,000–12,000 BTU (SACC)
Portable · inverter · No permanent mount · inverter
When a window mount isn’t an option, this inverter portable is one of the few that actually cools like its rating instead of falling short.
Find on AmazonEstimate only, from a simplified ≈20 BTU/sq-ft model with documented adjustments. Confirm with a Manual J load calculation before buying or installing equipment.
Start from about 20 BTU per square foot in a temperate climate, then adjust: strong sun (+10%), poor insulation (+15%), a hot climate (+25%), ceilings over 8 ft, each occupant beyond two (+600 BTU), and a kitchen (+4,000 BTU) all raise the load. Enter your exact room above to get the adjusted BTU, tonnage, and recommended unit type.
Divide the BTU by 12,000 — one ton of cooling equals 12,000 BTU. So a 12,000 BTU unit is 1 ton, 24,000 BTU is 2 tons, and 36,000 BTU is 3 tons. The calculator shows both the BTU and the tonnage for your room.
Roughly 20 BTU per square foot for an average-insulation room in a temperate climate. Sunny, poorly insulated, or hot-climate rooms push toward 25 BTU per square foot or more, while a well-shaded, well-insulated room in a mild climate can need a little less.
An oversized AC short-cycles — it cools the air quickly but shuts off before it removes enough humidity, leaving the room cold and clammy. The frequent on/off cycling also wastes energy and wears the compressor faster. Right-sizing matters more than simply buying the largest unit.
Yes — floor area alone is only the starting point. Ceilings above the standard 8 ft add volume to cool, poor insulation adds about 15%, strong direct sun adds about 10%, each person beyond two adds ~600 BTU, and a kitchen adds ~4,000 BTU for appliance heat. The calculator folds all of these in.
A hot climate raises the cooling load by roughly 25% versus a temperate one, so the same room needs more BTU further south. For heating, the reverse is true: cold climates need a larger furnace (about 50–60 BTU per square foot) than a mild one.