Mini-Split Sizing Calculator

Size ductless mini-split systems based on room dimensions, insulation quality, windows, and climate zone.

Inputs

Room Size

sq ft

Ceiling Height

Window Area

sq ft

Insulation Quality

IECC 2021: Poor <R-13; Average R-13–19 walls/R-30 ceiling; Good R-20+ walls/R-38+ ceiling

Climate Zone

Tab to move between fields

Results

Required BTU

10,600 BTU/hr

Recommended Size

1 tons

≈ 11 adults

Typical SEER Rating20

Est. Annual Cooling Cost$103.00

How to Use This Calculator

Enter Room Size, Ceiling Height, and Window Area.
Set Insulation Quality and Climate Zone.
Review Required BTU (BTU/hr) and Recommended Size (tons).
Use Typical SEER Rating and Est. Annual Cooling Cost ($) to inform your decision.

How the result changes with Room Size

Room Size	Required BTU	Recommended Size
545	14,225 BTU/hr	1.5 tons
1,783	45,175 BTU/hr	4 tons
3,268	82,300 BTU/hr	7 tons
4,505	113,225 BTU/hr	9.5 tons

What each input means

Room Size: Floor area of the room or zone to be conditioned.
Ceiling Height: Ceiling height. Rooms taller than 8 ft require proportionally more capacity.
Window Area: Total window and glass door area in the room. Adds solar heat gain load.
Insulation Quality: Wall and ceiling insulation quality per IECC 2021 and ASHRAE 90.1. Poor (1): uninsulated or R-11 walls; Average (2): R-13 to R-19 walls, R-30 ceiling; Good (3): R-20+ walls, R-38+ ceiling per IECC Climate Zone 4–5.
Climate Zone: Climate severity: 1 = Mild (coastal), 2 = Moderate, 3 = Average, 4 = Cold, 5 = Very Cold.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Room Size = 400, Ceiling Height = 8, Window Area = 30, Insulation Quality = 2 = 5 input(s) provided
Calculate Required BTU
Required BTU
10600 = 10600
Calculate Recommended Size
Recommended Size
1 = 1
Calculate Typical SEER Rating
Typical SEER Rating
20 = 20
Calculate Est. Annual Cooling Cost
Est. Annual Cooling Cost
103 = $103

Engine last updated August 5, 2026. Checked against 1 independently-derived test — how we verify calculators.

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