BTU Calculator for Air Conditioners
What size air conditioner do you need? Enter the size of the room, the ceiling height, how sunny it is, and how many people use it to find the BTU per hour you need, and the nearest size you can buy.
Cooling capacity needed (BTU/h)
7,000
Check the highlighted fields to see your result.
- In frigorías
- 1,750
- Nearest standard size
- 8,000 BTU/h (2,000 fg)
- In tons
- 0.58
Results are estimates for information only and do not constitute financial, medical, or legal advice.
How it works
The calculator starts from the ENERGY STAR sizing chart, which gives the cooling capacity for each range of floor area, assuming an 8-foot ceiling. Then it adjusts: 10% more for a very sunny room, 10% less for a shaded one, 600 BTU per hour for each person beyond two, and extra for a kitchen. Taller ceilings add capacity in proportion.
The formula
BTU/h = chart value × ceiling factor × sun factor + 600 × (people − 2) + 4,000 if kitchen
1 ton = 12,000 BTU/h · 1 kW = 3,412 BTU/h.
Worked example
A 300 sq ft living room with an 8 ft ceiling, normal sun, and 2 people.
- Chart value for 250 to 300 sq ft: 7,000 BTU/h.
- No adjustments: normal sun, 2 people, not a kitchen.
- Result: 7,000 BTU/h, so the nearest standard size is an 8,000 BTU unit.
- If the room were very sunny: 7,000 × 1.10 = 7,700 BTU/h, still an 8,000 BTU unit.
Sources and cautions
The chart and the sun and people adjustments come from ENERGY STAR:How to choose the right-sized window ACand itsroom air conditioner guide. The extra for a kitchen is a common rule of thumb. This is an estimate: rooms with large windows, poor insulation, or heat-producing equipment may need more, and an HVAC professional can calculate the exact load.
Frequently asked questions
How many BTUs do I need to cool a room?
It mostly depends on the area. For a room of 300 square feet, ENERGY STAR suggests about 7,000 BTU per hour. Very sunny rooms need about 10% more, shaded rooms about 10% less, and each person beyond two adds about 600 BTU per hour. Kitchens need more because of the heat from cooking.
What happens if the air conditioner is too big or too small?
A unit that is too small will run all the time and struggle to cool the room. A unit that is too big cools the air quickly and shuts off before it removes enough humidity, which leaves the room cold but damp. Choosing the right size saves energy and feels more comfortable.
How do I convert BTU to tons or kilowatts?
One ton of refrigeration is 12,000 BTU per hour, so a 12,000 BTU unit is 1 ton. One kilowatt is 3,412 BTU per hour. This is the cooling power of the unit, not the electricity it uses, which is much lower.
Does this work for a whole house?
It is meant for a single room or open space. For a whole house or central air, the right size also depends on insulation, windows, climate, and ducts, so ask an HVAC professional for a load calculation.