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Mini Split Size Calculator: Find the Right Ductless BTU & Tonnage for Your Room

Enter your room dimensions, climate, and details below to get the correct ductless mini split sizein both BTU and tons. Mini splits are inverter-driven and come in standard capacities from 9,000 to 48,000 BTU, so we match your room's cooling load to the nearest nominal size.

Mini Split Size Calculator

Feet
InchesSwitch between feet and inches measurement units
This form calculates the optimal air conditioner size for your room based on dimensions, climate, and various factors.

Room Dimensions

Room Dimensions Input Fields
ft
ft
ft

Location & Room Type

Location and Room Type Selection

Room Characteristics

Room Characteristics

Environmental Factors

Environmental Factors

Heat-Generating Appliances

Heat-Generating Appliances

Recommended Mini Split Size

Room Area:144.00 sq ft
Room Volume:1440.00 cubic ft
Room Cooling Load:6,667 BTU

Recommended Mini Split Size

0.75 Ton

9,000 BTU (0.75 Ton)

What This Means

Based on your room's dimensions and conditions, we recommend a 9,000 BTU (0.75 Ton) ductless mini split. This size will cool your room while maintaining proper humidity levels. The calculation is based on your local climate conditions and applies a combined adjustment factor of 1.79x.

Note: Mini splits are inverter-driven, so the compressor modulates to match demand. Slight oversizing is acceptable because the unit simply runs at a lower speed.

This calculator uses the same room cooling-load engine as our main AC tonnage calculator, then matches it to standard ductless mini split sizes. Inspired by ASHRAE standards and ACCA Manual J.

What Size Mini Split Do I Need?

To size a ductless mini split, calculate your room's cooling load (room square footage × 20–25 BTU, adjusted for climate, ceiling height, sun, and occupancy) and then round to the nearest standard mini split capacity: 9,000, 12,000, 18,000, 24,000, 30,000, 36,000, or 48,000 BTU. A typical 300 sq ft room needs a 12,000 BTU (1 ton) mini split.

Because mini splits use inverter compressors that modulate their output, slight oversizing is acceptable — the unit simply runs at a lower speed rather than short-cycling. Use the calculator above for a number tailored to your climate zone.

Mini Split Size by Room Size (Quick Reference)General ductless sizing at 20–25 BTU per sq ft. Enter your climate zone above for an exact recommendation.
Room Size (sq ft)Mini Split Capacity (BTU)Tonnage
150 – 350 sq ft9,000 BTU0.75 Ton
350 – 500 sq ft12,000 BTU1 Ton
500 – 750 sq ft18,000 BTU1.5 Tons
750 – 1,000 sq ft24,000 BTU2 Tons
1,000 – 1,500 sq ft30,000 – 36,000 BTU2.5 – 3 Tons

How Mini Split Sizing Works

A ductless mini split serves a single room or zone with no duct losses, so the sizing math is the same room cooling-load calculation used by our main AC size calculator. We start with your room's square footage, apply a baseline of about 22 BTU per square foot, then adjust for ceiling height, climate zone, sun exposure, insulation, occupants, and appliances.

The one difference from a central system is the final step. Mini splits are manufactured in fixed nominal capacities (9k, 12k, 18k, 24k, 30k, 36k, 48k BTU), so we snap your calculated load up to the nearest available size rather than rounding to a generic quarter-ton.

Want the full formula? See our methodology page. For a whole-house ducted system instead, use the split AC tonnage calculator, or for a single-room plug-in unit try the window AC BTU calculator.

Frequently Asked Questions

What size mini split do I need?

Multiply the room's square footage by 20-25 BTU per square foot (higher for hot climates, sun-facing rooms, or high ceilings), then snap up to the nearest nominal mini split size: 9,000, 12,000, 18,000, 24,000, 30,000, or 36,000 BTU. A 350 sq ft bedroom typically needs a 9,000-12,000 BTU head. The calculator above runs this with your exact climate zone and room details.

How many square feet will a 12,000 BTU mini split cool?

A 12,000 BTU (1 ton) mini split comfortably cools about 450-550 square feet in a moderate climate, or closer to 400-450 square feet in hot southern climates. That makes it the go-to size for large bedrooms, master suites, and small living rooms. If the space has vaulted ceilings or big west-facing windows, treat it as the smaller end of that range.

What size mini split do I need for 1,000 square feet?

For an open 1,000 sq ft space in a moderate climate, you need roughly 22,000-25,000 BTU, which maps to a 24,000 BTU (2 ton) single-zone unit - or 30,000 BTU in a hot climate. But if the 1,000 sq ft is divided into separate rooms, one head won't reach them all; a multi-zone system with two or three smaller heads is the correct design.

How do I convert mini split BTU to tonnage?

Divide the BTU rating by 12,000. A 9,000 BTU mini split is 0.75 tons, 12,000 BTU is 1 ton, 18,000 BTU is 1.5 tons, 24,000 BTU is 2 tons, and 36,000 BTU is 3 tons. Mini split tonnage means exactly the same thing as central AC tonnage - it's the same unit of cooling capacity.

What is a good SEER rating for a mini split?

Mini splits are the most efficient AC type sold. The federal minimum is around 14.3-15.2 SEER2 depending on region, but mainstream mini splits rate 18-25 SEER2, and premium single-zone units reach 30+ SEER2. Anything at 20 SEER2 or above is a genuinely efficient pick; below 17 you're giving up the technology's main advantage.

Can one mini split cool an entire house?

Only if the house is small and open-plan. A single wall head can't push air around corners or into closed bedrooms. For whole-house coverage, use a multi-zone mini split system (one outdoor unit driving 2-5 indoor heads sized per room) or a ducted central system. Size each zone from its own room load, not the house total divided evenly.

Do mini splits heat as well as cool?

Most mini splits sold today are heat pumps, so yes - they both heat and cool. Cold-climate models maintain full heating output down to around 5°F and keep working below -15°F. If you'll rely on one for winter heating, size it for the larger of the heating and cooling loads, and check its rated heating capacity at low temperature, not just the nominal BTU.