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
36,000 BTU
Recommended unit
36,000 BTU
Tonnage
3 ton
Furnace (heating)
76,000 BTU
Best unit type
Central AC / ducted system
Alternative: Multi-zone mini-split, Two or more zoned units
Real, widely available units in the 24,000 – 36,000 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
2–5 zones · up to ~48k BTU
Multi-zone mini-split · DIY · Quick-connect · self-install warranty
Cool several rooms from one outdoor unit, each with its own thermostat, using the same DIY quick-connect line sets — the easiest multi-zone to self-install.
Find on AmazonBest value
2–4 zones
Multi-zone mini-split · Lower cost per zone
A cost-effective multi-head system when you want independent control of several rooms and don’t need DIY line sets.
Find on AmazonBudget pick
2–4 zones
Multi-zone mini-split · heat pump · Cools + heats every zone
Multi-zone heat-pump comfort at a value price, from the same line as our single-zone best-overall pick.
Find on AmazonOne outdoor condenser feeds two or more indoor heads — right when you’re cooling several rooms rather than one big space.
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.