BTUCalc

What size AC do I need?

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

48,000 BTU

Recommended unit

48,000 BTU

Tonnage

4 ton

Furnace (heating)

101,000 BTU

Best unit type

Central AC / ducted system

Alternative: Multi-zone mini-split

Recommended central ac / ducted

Real, widely available units in the 36,000 BTU (3 tons) and up 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

Carrier · Trane · Lennox

2–5 ton condensers

Central AC · pro install · Premium efficiency & dealer networks

The premium tier for whole-home central AC — highest efficiency options and the largest professional dealer/service networks. Priced and installed per quote.

Get quotes from local dealers

Best value

Goodman

2–5 ton condensers

Central AC · pro install · Value-leader central condensers

The value leader in central AC — solid, widely serviced equipment at a lower installed cost than the premium brands.

Get quotes from local dealers

At this capacity you want a ducted central system — it must be sized with a Manual J load calculation and installed by a licensed HVAC contractor. There is no DIY buy-and-plug option, so get quotes from local dealers rather than buying online.

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.

BTU by room size

10 × 10 room10 × 12 room12 × 12 room12 × 14 room12 × 16 room12 × 20 room14 × 16 room15 × 15 room16 × 16 room16 × 20 room20 × 20 room20 × 24 room

BTU by square footage

250 sq ft500 sq ft750 sq ft1,000 sq ft1,200 sq ft1,500 sq ft1,800 sq ft2,000 sq ft2,200 sq ft2,500 sq ft3,000 sq ft

Room size by BTU

5,000 BTU6,000 BTU8,000 BTU10,000 BTU14,000 BTU15,000 BTU

Room size by AC tonnage

1 Ton AC1.5 Ton AC2 Ton AC2.5 Ton AC3 Ton AC4 Ton AC5 Ton AC

Frequently asked questions

What size air conditioner do I need for my room?

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.

How do I convert BTU to tons of cooling?

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.

How many BTU do I need per square foot?

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.

What happens if my AC is too big for the room?

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.

Does ceiling height, insulation, or sun change the BTU I need?

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.

Do I need a bigger unit for a hot climate?

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.