BTU Calculator
Find the air conditioner size in BTU/h and kW for a room, using the ENERGY STAR sizing chart.
A rule-of-thumb guide for room air conditioners based on the ENERGY STAR chart. Ceiling height, insulation, windows and climate also matter; a professional load calculation is best for central systems.
About this tool
Enter the room dimensions, how sunny the room is, how many people usually use it and whether it is a kitchen. The calculator looks up the ENERGY STAR room air conditioner chart, applies its adjustments for sun, shade, occupants and kitchens, and shows the cooling capacity in BTU per hour and kilowatts.
Frequently asked questions
The ENERGY STAR chart gives 5,000 BTU/h for 100–150 ft², 6,000 for 150–250 ft², 8,000 for 300–350 ft², 10,000 for 400–450 ft² and 12,000 for 450–550 ft².
12 × 15 ft is 180 ft², which falls in the 150–250 ft² band, so ENERGY STAR suggests 6,000 BTU/h (about 1.76 kW). If the room is very sunny, add 10% for 6,600 BTU/h.
ENERGY STAR advises reducing capacity by 10% for a heavily shaded room, increasing it by 10% for a very sunny room, adding 600 BTU/h for each person above two who regularly uses the room, and adding 4,000 BTU/h if the unit is used in a kitchen.
1 BTU/h is 0.293 watts, so multiply BTU/h by 0.000293 to get kW. A 9,000 BTU/h unit is about 2.6 kW and a 12,000 BTU/h unit (one ton of cooling) is about 3.5 kW.
Related tools
Insulation U-Value CalculatorCalculate the U-value and R-value of a wall, roof or floor from insulation thickness and λ — and the thickness you need.Power Converter — hp to kWConvert horsepower to kW and back — mechanical hp, metric PS, watts, BTU/h and kcal/h in one place.Electricity Cost CalculatorFind out what an appliance costs to run per day, month and year from its wattage and your electricity price.Unit Price CalculatorCompare two products by price per gram, millilitre or item to see which is the better deal.Firewood Energy CalculatorHow many kWh of heat you get from firewood — by sacks or weight, moisture content and stove efficiency — and what the same heat costs as electricity.Square Footage CalculatorCalculate the area of a room or space in square feet, square metres and square yards — and what it will cost.