Enter your Room Length, Room Width, Ceiling Height, Sun Exposure, Insulation Quality, and a few other room details, and this Window Air Conditioner Size Calculator figures out exactly how many BTUs your space actually needs — so you're not sweating through an underpowered unit or freezing in an oversized one.
Recommended BTU
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Room Area
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Base BTU (20 BTU/sq ft)
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Total Adjustments
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BTU stands for British Thermal Unit and measures the amount of energy needed to raise one pound of water by one degree Fahrenheit. For air conditioners, BTU indicates cooling capacity - higher BTU means more cooling power.
An undersized AC unit will struggle to cool your room effectively, run constantly, consume more energy, and may overheat from overworking. It will also fail to remove adequate humidity, making the room feel uncomfortable.
An oversized AC unit will cool the room too quickly without removing enough moisture, creating a clammy, uncomfortable environment. It will also cycle on and off frequently, wasting energy and reducing the unit's lifespan.
Multiply the room's length by its width in feet. For example, a room that is 12 feet long and 10 feet wide has 120 square feet. Always measure the actual floor space, excluding closets or alcoves.
Key factors include ceiling height, number of occupants, sun exposure, insulation quality, room type (kitchens need more cooling), and floor level. Upper floors typically require more cooling capacity than ground floors.
Portable ACs are generally less efficient than window units, so you may need 20-30% more BTU capacity. They also lose efficiency due to heat generated by the internal compressor and less effective air circulation.
Heat pump window units can both cool and heat your room, making them versatile year-round solutions. However, they're typically more expensive and may have slightly lower cooling efficiency compared to cooling-only models.
This calculator provides reliable estimates based on industry standards and common factors. However, unique situations like unusually high ceilings, excessive heat sources, or extreme climate conditions may require professional assessment for optimal results.