Mini Split Sizing Calculator
What size mini split do I need? Use our free BTU calculator and sizing chart to find the perfect capacity for your space.
Why proper sizing matters
Comfort
An oversized unit short-cycles, creating temperature swings. An undersized unit can't keep up on extreme days.
Efficiency
Properly sized systems run longer cycles at lower power, using less energy and reducing your utility bills.
Longevity
Units that cycle on and off frequently wear out faster. Right-sized systems last longer with less maintenance.
The Manual J method
Manual J is the industry-standard calculation method for determining heating and cooling loads. It considers dozens of factors to calculate the exact BTU requirements for your space.
What Manual J considers
- ✓Square footage and room layout
- ✓Ceiling height and total volume
- ✓Insulation levels in walls, ceilings, and floors
- ✓Window size, type, and orientation
- ✓Number of occupants and heat-generating appliances
- ✓Local climate and temperature extremes
- ✓Air infiltration and ductwork (if applicable)
Use our free Manual J calculator
Calculate your loadHow Many BTU Per Square Foot Do I Need?
As a general rule of thumb, you need 20-30 BTU per square foot for cooling and heating. However, this varies significantly based on your specific conditions. Use our mini split sizing chart below for quick estimates:
Mini Split Sizing Chart
Important: These are rough estimates only. Always use a proper Manual J calculation for accurate sizing.
| Room size | Approximate BTUs | Typical tonnage |
|---|---|---|
| 150–250 sq ft | 6,000 BTU | 0.5 Ton |
| 250–400 sq ft | 9,000 BTU | 0.75 Ton |
| 400–550 sq ft | 12,000 BTU | 1 Ton |
| 550–750 sq ft | 18,000 BTU | 1.5 Ton |
| 750–1,000 sq ft | 24,000 BTU | 2 Ton |
| 1,000–1,400 sq ft | 30,000 BTU | 2.5 Ton |
| 1,400–1,800 sq ft | 36,000 BTU | 3 Ton |
Based on average insulation, 8-foot ceilings, and moderate climate. Your actual requirements may vary significantly.
Common sizing mistakes
“Bigger is better”
An oversized unit will short-cycle, failing to dehumidify properly and wasting energy. It's like driving by constantly tapping the gas and brake.
Using square footage alone
A 500 sq ft room with poor insulation and west-facing windows needs much more capacity than a well-insulated 500 sq ft room.
Ignoring climate zone
A house in Phoenix needs different sizing than the same house in Seattle, even with identical square footage and insulation.
Multi-zone systems
When using a multi-zone system, calculate the load for each zone separately, then ensure your outdoor unit has enough capacity to handle the combined load.
Multi-zone sizing tips
- •Calculate Manual J for each individual zone
- •Outdoor unit capacity should be 100–130% of total indoor unit capacity
- •Don't assume all zones will run at maximum simultaneously
- •Consider diversity factor — not all rooms reach peak load at the same time
Need help sizing your system?
Our team can help you determine the perfect system size for your space. Use our calculator or give us a call for personalized assistance.