What size air conditioner for 300 square feet?
Around 10,000 to 12,000 BTU for a typical living room.
A 300 sq ft living room with an 8 ft ceiling needs roughly 9,000 to 12,000 BTU/h, which is 0.75 to 1 ton. A 12,000 BTU unit is the usual choice.
The calculation broken down
A 300 sq ft living room, 8 ft ceiling, average insulation, three people, 40 sq ft of south-facing glazing with blinds and 300 W of appliances running:
Swipe to see the whole table
| Item | Watts | Where it comes from |
|---|---|---|
| Envelope and ventilation | 2,787 | 69.7 m³ x 40 W/m³ |
| Occupants | 360 | 3 people x 120 W |
| Solar gain | 286 | 3.72 m² x 110 W/m² x 0.7 |
| Appliances and lighting | 300 | TV, computer, lights |
| Subtotal | 3,733 | |
| 10 % margin | 373 | |
| Total | 4,106 W | = 14,011 BTU/h = 1.17 tons |
Open-plan kitchen
This is the most common modern layout and the most underestimated. An open kitchen adds the appliance load and, above all, the heat of cooking: an oven can add 1,000-2,000 W to the space while it runs.
If the space is open, calculate the whole volume, not just the seating area.
One unit or two
For 300 sq ft in a single room, one well-placed unit is usually enough. If the plan is L-shaped or has partitions, two smaller units distribute better than one large one, because cold air does not turn corners by itself.
Estimated running cost
A 12,000 BTU unit of average efficiency draws about 1,100-1,300 W. At 8 hours a day and $0.17/kWh, that is roughly $1.63 a day, about $49 a month of heavy use.
Sources and methodology
Conversions use exact constants: 1 BTU/h = 0.29307107 W and 1 frigorie/h = 1 kcal/h = 1.163 W. The component sizing model (load per volume by insulation level, 120 W per person, solar gain by glazed area) is set out in full on the air conditioner size calculator. It is a guideline estimate: a professional heat-load calculation considers considerably more variables.
Frequently asked questions
How many BTU do I need for 300 square feet?
9,000 to 12,000 BTU/h under normal conditions, and up to 14,000 with strong sun, several occupants and appliances running.
Is 12,000 BTU enough for 300 sq ft?
In most cases yes, with average insulation and some shade during peak hours. On a top floor facing west it may fall short.
How many tons for 300 square feet?
About one ton (12,000 BTU/h) for a typical room, rising to 1.25 tons for an exposed space.
What if the living room is open to the kitchen?
Calculate the whole open volume and add the cooking load: an oven can contribute 1,000-2,000 W while it runs.
One big unit or two small ones?
In a single room, one well-placed unit. In L-shaped plans or spaces with partitions, two units distribute the cold air better.