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
24,000 BTU
Recommended unit
24,000 BTU
Tonnage
2 ton
Furnace (heating)
50,000 BTU
Best unit type
Single-zone mini-split
Alternative: Large window unit
Real, widely available units in the 12,000 – 24,000 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
12k / 18k / 24k BTU
Ductless mini-split · heat pump · Cools + heats · strong all-rounder
A consistent independent favorite — efficient inverter heat pump that both cools in summer and heats in winter, at a mid-market price.
Find on AmazonBest value
12k / 18k / 24k BTU
Ductless mini-split · DIY · Pre-charged quick-connect · warranty holds on self-install
The only mainstream line with true pre-charged quick-connect line sets, so a homeowner can install it without a vacuum pump — and keep the full warranty.
Find on AmazonBudget pick
12k / 18k / 24k BTU
Ductless mini-split · Lowest entry price in the class
The budget way into a ductless heat pump. Field-charging and a licensed install get you the longer warranty.
Find on AmazonMini-splits mount permanently and need a small wall penetration; DIY kits are homeowner-installable, others want an HVAC tech.
Estimate 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.