Ac Size Calculator
Free Ac size tool for home. Enter your details to get instant, tailored results and guidance. Get results you can export or share.
Reviewed by Daniel Agrici, Founder & Lead Developer
Formula
BTU = Sq Ft × 20 × Ceiling Factor × Sun Factor × Insulation Factor × Climate Factor
Start with 20 BTU per square foot as the base. Adjust upward for ceilings above 8 feet, heavy sun exposure, poor insulation, and hot/humid climates. Adjust downward for shaded rooms, good insulation, and cool climates. The suggested unit size rounds up to the nearest standard AC size. Monthly running cost assumes 8 hours/day at $0.13/kWh with an EER of 10.
Worked Examples
Example 1: Standard Bedroom
Problem:350 sq ft bedroom, 8 ft ceilings, average sun exposure, average insulation, moderate climate.
Solution:Base BTU: 350 × 20 = 7,000\nSun adjustment: ×1.0 = 7,000\nInsulation: ×1.0 = 7,000\nClimate: ×1.0 = 7,000\nSuggested unit: 8,000 BTU (next standard size up)\nTon equivalent: 0.58 tons
Result:7,000 BTU needed | 8,000 BTU suggested unit
Example 2: Large Living Room in Hot Climate
Problem:600 sq ft living room, 10 ft ceilings, heavy sun, poor insulation, hot climate.
Solution:Base BTU: 600 × 20 = 12,000\nCeiling (10/8): × 1.25 = 15,000\nHeavy sun: × 1.15 = 17,250\nPoor insulation: × 1.2 = 20,700\nHot climate: × 1.2 = 24,840\nSuggested: 24,000 BTU (2 ton unit)
Result:24,840 BTU needed | 24,000 BTU (2 ton) unit
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy