Mini Split Calculator
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 June 3, 2026 by our expert review team
Mini Split Sizes and Coverage
BTU| 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.
Expert Contributors
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 June 2026
How we verify our calculatorsMini Split Zones Need Separate Loads
A ductless system can share one outdoor unit, but each indoor head still serves a specific room or zone. Size the head for that room first, then check the outdoor unit and connected capacity with the manufacturer and a qualified HVAC pro.
Pro Tips
Round to the next available indoor head size, then confirm the match with Manual J and the manufacturer's equipment tables.
Each indoor head serves one zone. Size the bedroom, living room, garage, or addition separately instead of averaging the whole house.
Start with our BTU calculator when you need a broader room-load estimate before choosing ductless equipment.
Multi-zone systems can connect several indoor heads to one outdoor unit, but connected capacity and line-set limits vary by model.
Place the indoor head where air can circulate across the room. Avoid corners, blocked walls, and spots directly above frequent seating.
Cold-climate performance depends on the specific heat pump model and outdoor temperature. Check the rated capacity at your design conditions.
Compare all heat pump types with our heat pump cost calculator for equipment, installation, and tax credit estimates.
How the Calculator Works
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
Quick Reference
- 1 ton
- 12,000 BTU/hr
- Base rate
- 25 BTU per sq ft
- Standard sizes
- 6K to 36K BTU
- Mini split SEER
- 20 to 30+
- Lifespan
- 15 to 20 years
Common Questions
What size mini split for a 12x12 room?
A 12x12 room is 144 sq ft. With average conditions, a 6,000 BTU head is often the first size to compare, while sun, poor insulation, or high ceilings can push the room higher.
How much does a mini split cost?
$1,700 to $5,000 installed is a common planning range for a single-zone system. Multi-zone work can cost more because each head, line set, and wall penetration adds labor.
Are mini splits more efficient than central AC?
Often, yes. Ductless systems avoid duct losses and many models have high SEER2/HSPF2 ratings, but efficiency depends on the exact equipment and installation.
Can a mini split heat and cool?
Yes. Ductless mini splits are heat pumps. Heating output falls as outdoor temperature drops, so cold-climate sizing should be checked carefully.
How many rooms can one mini split cover?
One outdoor unit can serve multiple indoor heads if it is a multi-zone model. Each head should still be sized for the room or zone it serves.
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?
Many systems last 15 to 20 years with routine filter cleaning, coil care, and professional service when needed.
Can I install a mini split myself?
Some kits are marketed to DIYers, but electrical work, permits, refrigerant handling, warranty rules, and local code can require licensed pros.
Real-World Mini Split Examples
Small Bedroom (10x12)
Good insulation, moderate climateA 6,000 BTU head is the likely planning size. Check the actual load if the room has big sunny windows.
Living Room (15x20)
Average insulation, warm climateA 1-ton head is a common fit for this kind of zone. Open layouts may need a wider load review.
Master Suite (16x14)
Average insulation, hot climateHot climate and sun exposure can move a bedroom above the smallest head size.
Garage Workshop (24x24)
Poor insulation, moderate climateGarages can swing high because of air leakage, door openings, and unfinished walls.
Mini Split Sizing Mistakes That Cost You Money
Sizing one head for several rooms
A single indoor head conditions the zone it can actually reach. Separate rooms usually need separate heads or a different distribution plan.
Oversizing the indoor head
Too much capacity can short-cycle and remove less humidity. Pick the next standard size above the load, then verify the match.
Ignoring cold-weather capacity
Heat pump output changes with outdoor temperature. Check rated heating capacity for your design temperature, not only the catalog headline size.
Ignoring insulation quality
Drafty walls, ceilings, and garage doors can dominate the load. Envelope fixes may reduce the size and improve comfort.
Not accounting for sun exposure
Sunny glass and west-facing rooms can need more cooling. Shaded rooms may not need the same head size as a similar sunny room.
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.