Last reviewed: November 11, 2026 · Reviewed by the Mercorp HVAC editorial team
For a room with standard 8-foot ceilings and average insulation, Carrier’s sizing chart puts a 12,000 BTU (1-ton) mini split at roughly 250 to 450 square feet. Square footage is only the starting point, though: sun exposure, the number of people, a kitchen, ceiling height and your climate all change the capacity you need.
Below you will find the sizing chart, the adjustments that apply to your space and a worked example.
Mini split size chart by square footage
| Room size (sq ft) | Recommended capacity (BTU) | Approx. tons |
|---|---|---|
| 100 to 150 | 5,000 to 6,000 | 0.5 |
| 150 to 250 | 6,000 to 9,000 | 0.5 to 0.75 |
| 250 to 350 | 9,000 to 12,000 | 0.75 to 1 |
| 350 to 450 | 12,000 to 15,000 | 1 to 1.25 |
| 450 to 600 | 15,000 to 18,000 | 1.25 to 1.5 |
Carrier also offers a rule of thumb: multiply the square footage by 25 BTU. It is a useful first estimate, but Carrier’s own examples do not always match its chart, so treat it as a ballpark figure.
Adjust for your space
For window units, ENERGY STAR recommends these adjustments to the base capacity. They are a reasonable reference for a mini split too:
- Heavily shaded room: reduce capacity by 10%.
- Very sunny room: increase capacity by 10%.
- More than two people regularly: add 600 BTU for each additional person.
- Kitchen: add 4,000 BTU.
Source: ENERGY STAR.
According to Carrier, you may also need more capacity if:
- Your ceilings are higher than 8 feet.
- The space is poorly insulated.
- You live where temperatures frequently top 90°F.
- The room has large windows with direct sun.
- It is an open floor plan connected to other areas, or a garage.
Worked example
A 13 × 16 ft bedroom (208 sq ft) that gets a lot of sun and where three people sleep:
- Base capacity from the chart: 6,000 to 9,000 BTU. Use 9,000 since the room is in the upper part of the range.
- Very sunny (+10%): 9,000 + 900 = 9,900 BTU.
- One person more than the two-person baseline (+600): 10,500 BTU.
- Result: pick the nearest available size that covers about 10,500 BTU, in this case a 12,000 BTU (1-ton) unit.
This is an estimate. For a whole house or rooms with a lot of glass, ask for a professional load calculation.
What happens if you pick the wrong size?
- Oversized: the unit cools quickly, shuts off and restarts soon after. This short cycling wastes energy, adds wear and removes humidity poorly. Carrier notes that oversizing is generally worse than undersizing.
- Undersized: the unit runs nonstop without reaching the set temperature, which raises energy use and wear.
Source: Carrier.
BTU and tons
| BTU/h | Tons |
|---|---|
| 9,000 | 0.75 |
| 12,000 | 1 |
| 18,000 | 1.5 |
| 24,000 | 2 |
| 36,000 | 3 |
When to get a Manual J load calculation
Carrier recommends always consulting an HVAC professional for a precise load calculation. The industry standard is ACCA Manual J, which accounts for your building envelope, windows, orientation and climate. Ask for one especially if you are planning a multi-zone system, if the space has a lot of glass or if you live in a very hot climate.
To choose the compressor type, read inverter vs non-inverter mini split. Once you know the size, see how much it costs to install a mini split.
Sources
- Carrier, “Calculating What Size Mini Split I Need”: Carrier.
- ENERGY STAR, “How To Choose the Right Sized Window AC”: ENERGY STAR.