Mini Split Size Calculator
Enter each room's size, sun, occupants and whether it's a kitchen and get the cooling BTU/h per zone and in total from ENERGY STAR's sizing chart and adjustments.
One zone per indoor head. Rooms with an 8 ft ceiling, as the chart assumes. The result updates as you type.
Cooling capacity by zone
14,400 BTU/h in total
1.2 tons (12,000 BTU/h per ton) across 2 zones
| Zone | Area | Chart | Adjustments | BTU/h |
|---|---|---|---|---|
| Living room | 320 ft² | 8,000 | +800 sun, +600 people | 9,400 |
| Bedroom | 144 ft² | 5,000 | — | 5,000 |
ENERGY STAR chart
| Area to be cooled (ft²) | Capacity needed (BTU/h) |
|---|---|
| 100 up to 150 | 5,000 |
| 150 up to 250 | 6,000 |
| 250 up to 300 | 7,000 |
| 300 up to 350 | 8,000 |
| 350 up to 400 | 9,000 |
| 400 up to 450 | 10,000 |
| 450 up to 550 | 12,000 |
| 550 up to 700 | 14,000 |
| 700 up to 1,000 | 18,000 |
| 1,000 up to 1,200 | 21,000 |
| 1,200 up to 1,400 | 23,000 |
| 1,400 up to 1,500 | 24,000 |
| 1,500 up to 2,000 | 30,000 |
| 2,000 up to 2,500 | 34,000 |
What this page cannot tell you
Your home's actual heat load. ENERGY STAR's chart is area-based guidance written for room air conditioners and assumes 8 ft ceilings; insulation, windows, climate, ceiling height and duct-free layout all change what a mini split needs. Installers size systems with a load calculation (ACCA Manual J). Heating capacity is a separate question this chart does not answer.
How to estimate mini split size by room
- Add a zone per indoor head. Name it and enter the room's length and width in feet.
- Set the sun. Heavily shaded takes 10% off; very sunny adds 10%.
- Enter the people. Each person beyond two who regularly uses the room adds 600 BTU/h.
- Tick kitchens. A kitchen adds 4,000 BTU/h.
- Read BTU per zone and total. With tons for comparing outdoor units.
10 situations where a mini split size calculator helps
Planning a multi-zone system
Get a figure for each head and the total for the outdoor unit.
Garage or workshop
A starting capacity for a single-zone unit.
Bonus room over a garage
Mark it sunny if it bakes in the afternoon.
Comparing installer quotes
See whether a proposed head is far above or below the chart.
Adding cooling to one room
A bedroom or office that the central system doesn't keep up with.
Kitchens and open plans
The kitchen adjustment is often forgotten.
Home offices with several people
Occupancy adds 600 BTU/h per person beyond two.
Avoiding an oversized unit
ENERGY STAR notes an oversized unit removes less humidity and leaves rooms clammy.
Converting to tons
Outdoor units are often described in tons; 12,000 BTU/h is one.
Budget planning
Total capacity drives equipment cost.
Where the figures come from — and what they are not
The capacities are ENERGY STAR's sizing chart from its Room Air Conditioners page ('Properly Sized Room Air Conditioners'): area to be cooled in square feet against capacity needed in BTUs per hour, from 5,000 BTU/h for 100–150 ft² to 34,000 BTU/h for 2,000–2,500 ft², 'calculated based on an 8-foot ceiling'. The adjustments are ENERGY STAR's own: reduce 10% if heavily shaded, increase 10% if very sunny, add 600 BTUs for each person beyond two who regularly occupies the room, and add 4,000 BTUs if the unit is used in a kitchen. The page applies the percentage first and then the additions; ENERGY STAR doesn't state an order.
A room whose area falls exactly on a boundary (such as 150 ft²) is given the lower row, since the chart reads '100 up to 150'. Rooms under 100 ft² or over 2,500 ft² are outside the chart and the page says so instead of guessing.
What this is not: ENERGY STAR wrote this chart for room air conditioners. It is a published area-based starting point, not a heat-load calculation. Ductless installers size systems with a load calculation (ACCA Manual J) that accounts for insulation, windows, climate, ceiling height and air leakage, and heating capacity is a separate question entirely. Use these numbers to plan and to sanity-check a quote. Everything runs in your browser.
Sources
- ENERGY STAR — Room Air Conditioners: Properly Sized Room Air Conditioners — Area-to-capacity chart and adjustments
Frequently asked questions
What size mini split do I need for 500 square feet?
ENERGY STAR's chart gives 12,000 BTU/h for 450–550 ft², before adjustments for sun, occupants or a kitchen.
How many BTU per square foot?
The chart isn't a fixed rate: it runs from about 33–50 BTU/h per ft² for small rooms down to under 15 for large areas.
What does one ton mean?
12,000 BTU per hour of cooling. A 24,000 BTU/h unit is 2 tons.
Should I round up to the next unit size?
The page doesn't choose equipment. ENERGY STAR warns that an oversized unit is less effective, so compare with a load calculation before buying.
Does it account for high ceilings?
No. The chart assumes 8 ft ceilings; taller rooms have more air to cool.
Is this a Manual J calculation?
No. It's ENERGY STAR's area-based chart. A Manual J load calculation is the proper sizing method.
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