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Space DetailsSingle room or entire home
Affiliate Disclosure: This calculator is free to use. Some product links are affiliate links. Product links and pricing are for the US market. BTU calculations work for any region.
How This Calculator Works
- Base BTU: Starts at 20 BTU per square foot (industry standard from ACCA Manual J simplified), then adjusts for ceiling height, climate, insulation, sun exposure, occupants, and kitchen heat load.
- Tonnage: 1 ton = 12,000 BTU. Central AC units are sold in half-ton increments (1.5, 2, 2.5, 3, 3.5, 4, 5 ton).
- Mini-splits: Sized by BTU. Common sizes are 9K, 12K, 18K, 24K, 36K BTU. Multi-zone systems can run multiple indoor heads off one outdoor compressor.
- This is an estimate. A proper Manual J load calculation by an HVAC contractor factors in window area, duct losses, and local design temperatures. Use this to verify contractor quotes are in the right ballpark.