AC BTU Calculator

About this calculator

This calculator estimates the cooling capacity, in BTU (British Thermal Units) per hour, an air conditioner needs to handle a room, based primarily on floor area with adjustments for factors like ceiling height, sun exposure, and number of occupants — the rule-of-thumb baseline is roughly 20 BTU per square foot before adjustments.

Homeowners shopping for a window or split-unit AC use it to avoid the two common mistakes: undersizing a unit that runs constantly without ever cooling the room properly, or oversizing one that cycles on and off too fast and leaves the air clammy. HVAC installers use the same logic as a quick sanity check before a full Manual J load calculation.