A common rule of thumb is 20 BTU per square foot for standard rooms with 8-foot ceilings. Adjustments: add 10% for sunny rooms or poor insulation; subtract 10% for heavily shaded rooms or excellent insulation. High ceilings (10+ ft) require 10–20% more BTU. Kitchens add 4,000 BTU for cooking heat. This calculator provides a more precise estimate by accounting for multiple factors.

Mini-splits come in standard sizes: 9,000 BTU (up to ~450 sq ft), 12,000 BTU (up to ~550 sq ft), 18,000 BTU (up to ~850 sq ft), 24,000 BTU (up to ~1,200 sq ft), 36,000 BTU (up to ~1,800 sq ft). The 12,000 BTU (1-ton) unit is the most common for bedrooms and small rooms. For whole-house cooling, 24,000–36,000 BTU is typical.

Yes — oversizing a mini-split causes short cycling (rapid on/off), poor humidity removal, uneven temperatures, and increased wear. An oversized unit will cool the room quickly, then shut off before completing a full dehumidification cycle. The room feels colder than the thermostat reading because the humidity remains high. Always size within 10–15% of calculated load.

Modern mini-splits (especially "cold-climate" or "hyper-heat" models from Mitsubishi, Daikin, LG, and Bosch) operate effectively down to -13°F to -22°F outdoor temperature. Standard mini-splits lose significant capacity below 20°F. If you're in a cold climate (Zone 5–7), look for units with HSPF2 ratings above 8.5 and cold-climate ratings.