ComfortSizer
Single-zone and multi-zone

Mini Split Size Calculator

What size mini split do you need? Add each room, set its size and sun, and see the head size for every zone and the outdoor unit for the whole system.

Rooms (zones)One indoor head per room
Load by room
All zones need –BTU/h
How we got this number

    100% private: the math runs in your browser and nothing is sent anywhere. Estimates for one room or open space up to 2,500 sq ft.

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    How mini split sizing works

    A ductless mini split has one outdoor unit and one indoor head per room (zone). Each head is sized to its own room, so the first step is the cooling load of every room. We use the ENERGY STAR room sizing chart and its adjustments: 10% more for very sunny rooms, 10% less for shaded ones, and 4,000 BTU more for kitchens.

    Indoor heads

    Wall heads are commonly sold in 6,000, 9,000, 12,000, 18,000 and 24,000 BTU sizes. Pick the next size up from the room's load. A head much bigger than the room cycles on and off and dehumidifies poorly.

    Outdoor unit

    For a single room, the outdoor unit comes matched to the head. For several rooms, the outdoor unit should cover the combined load. Many multi-zone systems allow the indoor heads to add up to somewhat more than the outdoor unit, because rooms rarely peak at the same time; check the maker's combination table for the exact pairings.

    Heating with a mini split? Heat pump output drops in cold weather. If heat is the main job, check each unit's capacity at 5 °F, and size the rooms with the heating BTU calculator too.

    This is an estimate for planning and shopping. Installers size systems with a Manual J load calculation, and that is what to use for a whole-house system.

    FAQ

    Questions

    What size mini split do I need for a 400 sq ft room?
    The ENERGY STAR chart puts 400 to 450 sq ft at 10,000 BTU with normal sun, so a 12,000 BTU head is the usual pick. In a very sunny room the load rises to about 11,000 BTU, still within a 12,000 BTU head.
    Can one mini split cool a whole house?
    One head cools the room it is in and, partly, open spaces next to it. Closed bedrooms need their own heads. That is why multi-zone systems exist.
    Should the indoor heads add up to the outdoor unit size?
    They should add up to about the outdoor unit's capacity. Many manufacturers allow the heads to total somewhat more than the outdoor unit, because rooms rarely need full cooling at the same time. Check the maker's combination table.
    How many zones can a multi-zone mini split have?
    Most residential multi-zone outdoor units drive 2 to 5 indoor heads. Larger homes often use two outdoor units.
    Is a 12,000 BTU mini split 1 ton?
    Yes. One ton of cooling is 12,000 BTU per hour, so a 24,000 BTU mini split is 2 tons.