Mini Split Sizing Guide
The standard HVAC rule of thumb is 20 BTU per square foot for average rooms at 8–9 ft ceiling height. Adjust for ceiling height, climate, sun, and insulation.
| Room Size | Typical BTU | Mini Split Size |
|---|---|---|
| Up to 350 sq ft | 7,000 BTU | 9,000 BTU (0.75 ton) |
| 350–550 sq ft | 10,000 BTU | 12,000 BTU (1 ton) |
| 550–800 sq ft | 14,000 BTU | 18,000 BTU (1.5 ton) |
| 800–1,200 sq ft | 18,000 BTU | 24,000 BTU (2 ton) |
| 1,200–1,800 sq ft | 24,000 BTU | 30,000–36,000 BTU |
Frequently Asked Questions
Start with 20 BTU per square foot. Multiply by room area, then adjust: add 10% for very sunny rooms, 15% for poor insulation, 10% for hot climates. Always round up to the nearest standard mini split size.
At 20 BTU/sq ft, a 1,000 sq ft space needs ~20,000 BTU. Round up to a 24,000 BTU (2-ton) system. If well-insulated and moderate climate, an 18,000 BTU unit may suffice.
Slightly oversizing (10–15%) is acceptable and preferable to undersizing. Significantly oversized units short-cycle (turn on/off rapidly), leading to humidity control issues, excess wear, and reduced efficiency.
One ton of cooling = 12,000 BTU/h. A 2-ton mini split = 24,000 BTU. The term ton originates from the amount of heat needed to melt one ton of ice in 24 hours.
In most US climates, size for cooling — heating is typically not the binding constraint. In very cold northern climates, check the mini split heating capacity at low outdoor temperatures (e.g., -15C specs).
This calculator provides an estimate based on Manual J simplified rules of thumb. For accurate sizing, especially for whole-home systems or unusual spaces, use a full Manual J load calculation performed by an HVAC professional.