Calculate the BTU cooling and heating capacity needed for your room or home based on size, climate, insulation, and more.
Room or area square footage
Ceiling height in feet
Typical occupancy of the room
Enter values above to see results
Cooling BTU = (sqft × 25 × roomFactor × climateMult × insulMult × winMult × ceilMult + sunAdd + peopleAdd) rounded to nearest 500sqftRoom or area square footageroomFactorAdjustment for room type (e.g. Kitchen: 1.4, Basement: 0.8)climateMultClimate multiplier (Hot: 0.9, Mild: 1.0, Cold: 1.15)insulMultInsulation multiplier (Poor: 1.25 → Excellent: 0.80)winMultWindow efficiency multiplierceilMultCeiling height multiplier (5% per ft above 8 ft)peopleAdd400 BTU per personThe base load of 25 BTU/sq ft is adjusted by factors for room type, climate, insulation quality, window type, sun exposure, ceiling height, and occupancy. Heating capacity is estimated at 25% above cooling capacity. Results are rounded to the nearest 500 BTU for practical unit sizing.
Choosing the right HVAC system or air conditioner starts with knowing how many BTUs you need. An undersized unit can't keep up on hot days, while an oversized unit wastes energy and fails to dehumidify properly. This BTU calculator accounts for room size, climate, insulation, windows, sun exposure, ceiling height, and occupancy to give you an accurate cooling and heating load estimate.
Enter your room's square footage and select the room type, climate zone, insulation quality, window type, sun exposure, ceiling height, and typical number of occupants. The calculator applies industry-standard adjustment factors to the base load of 25 BTU/sq ft and rounds to the nearest 500 BTU for practical unit selection.
Rather than a simple square-footage lookup, this calculator applies multiple real-world factors that significantly affect your actual cooling and heating load. It also recommends a specific unit size (window unit, mini-split, or central AC tonnage) to help you shop with confidence.
Don't just use the 20 BTU/sq ft rule of thumb without adjustments — climate, insulation, and ceiling height can change your requirement by 30% or more. Also avoid buying the largest unit available 'just in case'; oversized systems are genuinely worse than correctly sized ones.
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