What size mini split do I need? Calculate the right ductless AC and heat pump size for any room. Get BTU recommendations, unit sizing, and cost estimates.
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Last updated March 2026 by our expert review team
| Size (BTU) | Coverage (sq ft) | Tonnage | Unit Cost |
|---|---|---|---|
| 6,000 | 150 - 250 | 0.5 | $700 - $1,200 |
| 9,000 | 250 - 400 | 0.75 | $800 - $1,500 |
| 12,000 | 400 - 550 | 1 | $1,000 - $2,000 |
| 18,000 | 550 - 800 | 1.5 | $1,500 - $2,500 |
| 24,000 | 800 - 1,100 | 2 | $2,000 - $3,500 |
| 36,000 | 1,100 - 1,500 | 3 | $3,000 - $5,000 |
Coverage assumes average insulation, standard 8 ft ceilings, moderate climate.
Ehsan Ghazanfari
Licensed Structural Engineer
FISE-certified structural engineer with 11+ years designing bridges, retaining walls, and foundations. MSc from Aalto University.
See full profileHawkin
Certified Cost & Estimating Professional
AACE-certified estimator working with 20+ insulation companies including the two largest franchises in America.
See full profileUpdated March 2026
How we verify our calculatorsAlways round up to the next standard size. A 10,500 BTU room needs a 12,000 BTU unit. Undersizing leads to constant running and higher bills.
Mini splits at SEER 20+ are 2 to 3 times more efficient than window units at SEER 10. The higher upfront cost pays back in 3 to 5 years.
For central HVAC sizing, use our BTU calculator for whole-house load estimates.
Multi-zone mini splits can serve 2 to 5 rooms from one outdoor unit. Each indoor head is sized independently.
Install the indoor unit high on the wall (7+ ft). Cool air falls naturally, and high mounting improves circulation.
Mini splits work as heat pumps too. They heat efficiently down to 5 degrees F (with hyper-heat models). Perfect for supplemental heating in cold climates.
Enter room dimensions, ceiling height, and number of occupants.
Select insulation quality, sun exposure, and climate zone to adjust the load calculation.
Get the recommended mini split size, tonnage, and installed cost estimate.
Formula
Base BTU = Room Area x 25 BTU/sq ft x sun x ceiling x insulation x climate + occupant load
Recommended size = next standard mini split size above the calculated BTU
What size mini split for a 12x12 room?
A 12x12 room (144 sq ft) needs a 6,000 to 9,000 BTU mini split with average insulation and moderate climate.
How much does a mini split cost?
$1,700 to $5,000 installed for a single-zone system. Multi-zone systems with 2 to 4 heads cost $3,000 to $10,000 installed.
Are mini splits more efficient than central AC?
Yes. Mini splits rate SEER 20 to 30 vs. central AC at SEER 14 to 20. No duct losses (which waste 20 to 30% in central systems).
Can a mini split heat and cool?
Yes. All modern mini splits are heat pumps. They cool in summer and heat in winter down to 5 degrees F (hyper-heat models) or 15 degrees F (standard).
How many rooms can one mini split cover?
One outdoor unit can power 2 to 5 indoor heads (multi-zone). Each head is independently controlled for different room temperatures.
Do mini splits need ductwork?
No. That is their main advantage. They only need a 3-inch hole through the wall for the refrigerant line, drain, and power cable.
How long do mini splits last?
15 to 20 years with annual maintenance (filter cleaning, coil inspection). Compressor warranty is typically 7 to 10 years.
Can I install a mini split myself?
The indoor unit and line set are DIY-friendly. But charging the refrigerant requires EPA 608 certification. Most jurisdictions require a licensed HVAC tech for the final connection.
A single 6,000 BTU wall unit handles this room easily. Total installed cost: $1,700 to $3,200.
A 1-ton mini split covers this space. The warm climate bumps the load above 9,000 BTU. Total installed cost: $2,500 to $5,000.
Hot climate and moderate sun push this room into 12,000 BTU territory. Total installed cost: $2,500 to $5,000.
Poor insulation on a large space needs a 2-ton unit. Total installed cost: $4,500 to $7,500.
Undersizing the unit
An undersized mini split runs constantly, never reaching the target temperature. Energy bills go up and the compressor wears out faster.
Oversizing the unit
An oversized unit short-cycles, turning on and off every few minutes. This wastes energy and causes poor dehumidification, leaving the air clammy.
Installing indoor unit too low on the wall
Mount the indoor head at least 7 feet high. Cool air falls naturally, and a low-mounted unit creates uneven temperatures with cold spots near the floor.
Ignoring insulation quality
Poor insulation increases BTU needs by 30% compared to average. A room with good insulation needs 10% less. Always assess insulation before sizing.
Not accounting for sun exposure
South-facing rooms with large windows need 10% more BTU. Shaded rooms need 10% less. Skipping this leads to under or oversizing.
Important Disclaimer
These estimates are for planning purposes only. Actual costs vary by location, material availability, and project complexity. Always get at least 3 local quotes. This calculator does not replace professional advice.