BTU Calculator
Get a transparent rule-of-thumb estimate for room cooling capacity. Adjust ceiling height, insulation, climate, sunlight and internal heat sources.
Your result
How the calculation works
Base cooling = floor area in ft² × 20 BTU/h per ft² × (height ÷ 8 ft). Multiply by insulation (0.85 / 1 / 1.2), climate (0.9 / 1 / 1.2) and sunlight (0.9 / 1 / 1.1). Add 600 BTU/h per occupant above two, and 4,000 BTU/h for a kitchen. Cooling tons = BTU/h ÷ 12,000.
Worked example
A 20 m² room with an 8 ft ceiling and typical assumptions has a base estimate of about 4,306 BTU/h, or 0.36 cooling tons. One extra occupant adds 600 BTU/h. These factors are declared planning assumptions, not equipment-selection rules.
Assumptions and limitations
The multipliers are simplified heuristics selected for this tool. They do not use weather records, window orientation, infiltration, humidity, solar gain, equipment schedules or wall construction. A zero-area room must not be interpreted as a valid equipment load.
This is an estimation tool, not a substitute for a professional HVAC load calculation. Oversizing can harm humidity control and efficiency. Ask a qualified professional to assess the full building and appropriate equipment.
Method reviewed 2026-10-07. Calculation standards · Report an issue