AC Size Calculator

Calculation Method

The calculator determines the required cooling capacity using these steps:

1. Base BTU = room area (sq ft) × 20 BTU per sq ft (standard cooling load)
2. Ceiling adjustment = increase by 10% for each foot above 8 ft standard height
3. Sun exposure = subtract 10% for heavy shade, add 10% for direct sun
4. Insulation = add 10% for poor insulation, subtract 10% for good insulation
5. Occupants = add 600 BTU per person beyond the first two
6. Room type = add 4,000 BTU for kitchens due to appliance heat
7. Floor level = add 10% for top floors (heat rises)

Common AC Sizes

• 5,000 BTU — small rooms up to 150 sq ft
• 8,000 BTU — rooms 300–350 sq ft
• 10,000 BTU — rooms 400–450 sq ft
• 12,000 BTU (1 ton) — rooms 450–550 sq ft
• 14,000 BTU — rooms 500–700 sq ft
• 18,000 BTU (1.5 ton) — rooms 700–1,000 sq ft
• 24,000 BTU (2 ton) — large spaces 1,000–1,400 sq ft

Tips

• An oversized unit cools quickly but cycles on and off frequently, reducing dehumidification and efficiency
• An undersized unit runs continuously, increasing energy costs and wear
• Energy Star rated units can save 10–15% on cooling costs
• Consider a unit's SEER rating — higher SEER means greater energy efficiency
• For very large spaces, multiple smaller units may cool more evenly than one large unit