Determine the precise cooling capacity required for your space.
Excellent (Modern build)
Average
Poor (Older home/Drafty)
Shady / North Facing
Normal Exposure
Very Sunny / West Facing
Recommended Capacity
0 BTU
0 Tons
Note: Round up to the nearest available unit size (9k, 12k, 18k, 24k, etc.)
How to Size Your Mini Split Correctly
Choosing the right size for a ductless mini-split system is critical for both comfort and energy efficiency. An undersized unit will run constantly without ever reaching the set temperature, while an oversized unit will "short cycle," turning on and off rapidly, which leads to poor dehumidification and premature wear on the compressor.
The standard industry rule of thumb is 20 BTUs (British Thermal Units) per square foot of living space. However, this base calculation must be adjusted for environmental factors like ceiling height, insulation quality, and local climate.
Key Factors Influencing BTU Requirements
Square Footage: The primary driver. Length × Width of the room.
Ceiling Height: Standard calculations assume 8-foot ceilings. If your ceilings are higher, you have more volume of air to cool.
Insulation: Poorly insulated walls or single-pane windows allow heat to seep in, requiring higher cooling capacity.
Sunlight: Rooms with large west-facing windows or heavy sun exposure need approximately 10% more cooling power.
Kitchens: Appliances generate significant heat. Always add 4,000 BTUs if the indoor unit is located in a kitchen.
Occupancy: Each person generates body heat. If more than two people regularly occupy the room, add 600 BTUs per additional person.
BTU to Tonnage Quick Reference Chart
Square Footage
BTU Capacity
Tonnage
150 – 250 sq ft
6,000 BTU
0.5 Ton
250 – 400 sq ft
9,000 BTU
0.75 Ton
400 – 650 sq ft
12,000 BTU
1.0 Ton
650 – 1,000 sq ft
18,000 BTU
1.5 Tons
1,000 – 1,400 sq ft
24,000 BTU
2.0 Tons
Example Calculation
If you have a 20′ x 20′ living room (400 sq ft) with 10-foot ceilings, average insulation, and it's quite sunny: