What size mini split do I need? (300 to 1,500 sq ft, BTU and tons)
To size a single-zone mini split, look up the room's floor area on the ENERGY STAR room chart, then take the next size the maker sells. A 500 sq ft room is 12,000 BTU/h on the chart, so a 12,000 BTU/h (1-ton) unit; 1,000 sq ft is 21,000 BTU/h, so a 24,000 BTU/h (2-ton) unit in a current lineup of 9,000, 12,000, 18,000, 24,000, 30,000 and 36,000 BTU/h. The table covers 300 to 1,500 sq ft; below it, one zone or several, heating, and cold climates.
1. What size mini split for 300 to 1,500 sq ft
Each area is looked up on the ENERGY STAR room chart (ENERGY STAR, Room Air Conditioners, "Room Air Conditioner Sizing" chart) as one open space with average sun and two people; ENERGY STAR says "the capacities are calculated based on an 8-foot ceiling". The next column is the smallest size at or above that figure in Fujitsu's Altair 500 single-room lineup, which lists "Size (kBTU/h): 9, 12, 18, 24, 30, 36". Tons = BTU/h / 12,000.
| Area (sq ft) | Chart band (sq ft) | Chart BTU/h | Next size | Tons | Very sunny: next size |
|---|---|---|---|---|---|
| 300 | 300 up to 350 | 8,000 | 9,000 BTU/h | 0.75 | 9,000 BTU/h |
| 400 | 400 up to 450 | 10,000 | 12,000 BTU/h | 1 | 12,000 BTU/h |
| 500 | 450 up to 550 | 12,000 | 12,000 BTU/h | 1 | 18,000 BTU/h |
| 600 | 550 up to 700 | 14,000 | 18,000 BTU/h | 1.5 | 18,000 BTU/h |
| 800 | 700 up to 1,000 | 18,000 | 18,000 BTU/h | 1.5 | 24,000 BTU/h |
| 1,000 | 1,000 up to 1,200 | 21,000 | 24,000 BTU/h | 2 | 24,000 BTU/h |
| 1,200 | 1,200 up to 1,400 | 23,000 | 24,000 BTU/h | 2 | 30,000 BTU/h |
| 1,500 | 1,500 up to 2,000 | 30,000 | 30,000 BTU/h | 2.5 | 36,000 BTU/h |
300 sq ft is 8,000 BTU/h, so the smallest size in this lineup, 9,000 BTU/h. 600 sq ft is 14,000 BTU/h, between two sizes, so 18,000 BTU/h. Other lines step differently: Fujitsu's Orion XLTH lists "Size (kBTU/h): 9, 12, 15, 18, 24", so check the steps of the line you are buying. The BTU to tons converter turns any size into tons and kW.
2. How to read it
The chart figure is for one space with average sun, two people and an 8 ft ceiling. The chart's own adjustments move it: very sunny x1.1, heavily shaded x0.9, +600 BTU/h for each person beyond two, +4,000 BTU/h for a kitchen. The last column shows how the very sunny figure can push a room to the next size. The AC BTU calculator applies all of them and a taller ceiling to your room.
3. One zone or several
A single-zone system is one outdoor unit and one indoor unit: Fujitsu sells the Altair 500 as a "single room mini-split system", each indoor unit with its own outdoor unit. A multi-zone system shares one outdoor unit between rooms. Mitsubishi Electric: "One multi-zone outdoor unit can connect up to eight indoor units, delivering individual temperature sensing and control to multiple zones." Either way, size each indoor unit for its own room with table 1; the 1,500 sq ft house guide shows a house room by room and why the rooms add up to more than the floor read as one space.
4. A mini split heats too
A mini split can be a heat pump or cooling-only: Mitsubishi describes its MUZ-GS heat pump as "a single-zone heating and cooling solution" and its MUY-GS as a cooling-only system for "climates where heating is unnecessary". With a heat pump, check the heating side too. The heat pump size calculator uses a published rule of 45-50 BTU/h per sq ft in zone 4 (HVACDirect.com, How to Size Your Air Conditioner or Heater, heating factor): with average insulation, 1,000 sq ft needs 47,500 BTU/h to heat against 21,000 to cool, and 500 sq ft needs 23,750 against 12,000. Where winters are cold, the heating figure can decide the size.
Heating capacity also changes with the weather outside. To earn ENERGY STAR's cold climate designation, a heat pump must keep at least 70 percent of its 47°F heating capacity at 5°F and reach a COP of 1.75 there. Makers state a heating operation range: 5°F to 75°F for the Altair 500, "-15°F to 75°F" for Fujitsu's Orion XLTH line. For a garage, the garage BTU guide sizes heating and cooling side by side.
Frequently asked questions
- What size mini split do I need for 500 sq ft?
- 12,000 BTU/h on the ENERGY STAR chart ("450 up to 550" sq ft), so a 12,000 BTU/h (1-ton) unit. If the room is very sunny the chart adds 10 percent, 13,200 BTU/h, and the next size is 18,000 BTU/h.
- What size mini split for 1,000 sq ft?
- 21,000 BTU/h on the chart ("1,000 up to 1,200" sq ft), so a 24,000 BTU/h (2-ton) unit if the 1,000 sq ft is one open space. If it is several rooms, each room gets its own figure and indoor unit; the 1,500 sq ft house guide adds rooms up.
- What size mini split for 1,500 sq ft?
- 30,000 BTU/h on the chart ("1,500 up to 2,000" sq ft), a 30,000 BTU/h (2.5-ton) unit as one open space; 23,000 BTU/h and a 24,000 BTU/h (2-ton) unit at 1,200 sq ft. A whole house is better sized room by room or by an installer's Manual J.
- What size mini split for a 2 car garage?
- Measure yours: we found no published standard size for a two-car garage that we could quote. On the room chart, 20 x 20 ft (400 sq ft) is 10,000 BTU/h, so the next size is 12,000 BTU/h; 24 x 24 ft (576 sq ft) is 14,000 BTU/h, so 18,000 BTU/h. To heat it, the garage BTU guide's heater formula gives more: 24,900-30,400 BTU/h for 24 x 24 ft well insulated at a 60°F rise.
- How many BTU do I need for a mini split? (BTU calculator)
- The AC BTU calculator reads the ENERGY STAR chart for any room and adds the chart's adjustments: very sunny +10 percent, heavily shaded -10 percent, 600 BTU/h per person beyond two, 4,000 BTU/h for a kitchen. Take that figure, then the next size in the lineup you are buying from.
- Can one outdoor unit run several rooms?
- Yes, with a multi-zone system. Mitsubishi Electric: "One multi-zone outdoor unit can connect up to eight indoor units, delivering individual temperature sensing and control to multiple zones." A single-zone system pairs one outdoor unit with one indoor unit, which is what table 1 sizes.
Sources
- ENERGY STAR (U.S. EPA), Room Air Conditioners: the room size to capacity chart (undated), read 2026-10-19.
- Fujitsu General (AIRSTAGE), AIRSTAGE Altair 500, single-room mini-split system (undated), read 2026-10-19.
- Fujitsu General (AIRSTAGE), AIRSTAGE Orion XLTH, single-room mini-split system (undated), read 2026-10-19.
- Mitsubishi Electric HVAC US, Wall-Mounted AC & Heating Units (undated), read 2026-10-19.
- Mitsubishi Electric HVAC US, Premier Wall-Mounted Single-zone Heat Pump, MUZ-GS (undated), read 2026-10-19.
- ENERGY STAR (U.S. EPA), Program Requirements for Heat Pumps, Eligibility Requirements (cold climate criteria) (Rev. February 2026), read 2026-10-19.
- HVACDirect.com, How to Size Your Air Conditioner or Heater (the BTU per sq ft by climate zone rule the heat pump calculator uses) (undated), read 2026-09-20.
The sizes are one maker's current single-zone lineup, read on the day shown; other lines step differently. Brand names are named only as the source of a figure, not as a recommendation.
More guides
- How many BTU do I need per square foot? (room size chart)
The ENERGY STAR room size to BTU chart with its adjustments, heating BTU and tons by home size and climate zone, and m² to kW at three insulation levels.
- How many BTU do I need for a bedroom? (12x12 and other room sizes)
A 12 x 12 bedroom is 5,000 BTU/h on the ENERGY STAR chart. Eight bedroom sizes with the sun, people and ceiling adjustments, m² to kW, and the unit class for each.
- How many BTU do I need for 1,000 sq ft? (200 to 1,200 sq ft, cooling and heating)
1,000 sq ft is 21,000 BTU/h on the ENERGY STAR chart (1.75 tons) and 32,500-55,000 BTU/h to heat by zone. 200 to 1,200 sq ft, with the adjustments.
- What size air conditioner do I need for a 1,500 sq ft house? (tons by home size)
The chart reads 1,500 sq ft as 30,000 BTU/h (2.5 tons); room by room the units add to 44,000. Both readings, 1,000-3,000 sq ft, and a seven-room example.
Last updated 2026-10-19. Sizing estimates from published charts and rules of thumb (ENERGY STAR, manufacturer guides), each with its source and date: a Manual J load calculation by an installer is the final word.