What size AC do I need for a room?

As a rule of thumb, a normal room up to about 150 sq ft needs a 1 ton AC, 150–250 sq ft a 1.5 ton, and 250–400 sq ft a 2 ton. Add capacity for top floors, strong sun, more people or heat-producing appliances.

How is AC tonnage calculated?

Start from the floor area adjusted for your climate and ceiling height, then add for occupants beyond two, sun exposure or a top floor, and heat sources, and round up to the nearest standard AC size.

Is a bigger AC always better?

No. An oversized AC cools fast but cycles on and off, cooling unevenly and removing less humidity. The right size runs longer and more efficiently.

Home · Tools · AC Tonnage

Home & utilities

AC Tonnage Calculator

Find the right air-conditioner size for a room. Enter the area and adjust for ceiling height, sun, occupants and heat sources, and you'll get the cooling load and the standard AC tonnage to buy.

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Room

Enter room as

Measured in

Length ft

Width ft

Ceiling height ft

Conditions

Climate

Occupants 2

Sun / position

Heat sources

Recommended AC—

Calculated cooling load—

Approx. cooling capacity—

Room area—

How it's calculated

The floor area is divided by a factor for your climate to get a base load, scaled for ceiling height, then capacity is added for each occupant beyond two, for sun or a top-floor position, and for heat-producing appliances. The total is rounded up to the nearest standard AC size. One ton of cooling is about 12,000 BTU/hr.

This is a planning rule of thumb. For glass-heavy rooms or unusual layouts, a professional heat-load (Manual J) calculation is more precise.

Frequently asked questions

Inverter or fixed-speed?

Sizing is the same; an inverter AC then modulates to run efficiently at part load.

What if I'm between sizes?

Round up — a slightly larger unit handles peak heat, but don't oversize by a full ton.

Does star rating change tonnage?

No — rating affects running cost, not the cooling capacity you need.

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