Mini-Split BTU Calculator
Enter your room details and get a cooling load in BTU/hr and tons, plus the nearest standard mini-split size, using the Department of Energy sizing rule.
How to size your mini split
Measure the room
Multiply length by width for floor area, and note the ceiling height. The rule assumes 8 feet; taller ceilings get a proportional bump.
Set the conditions
Pick the climate you live in, how much sun the room gets, and how well the walls and windows insulate. Hot, sunny, and poorly insulated rooms need more capacity.
Count the people and the stove
Each person beyond the first adds body heat, and cooking equipment adds a lot. Enter the usual headcount and tick the kitchen box only for rooms with cooking appliances.
Pick the nearest standard unit
Mini-splits come in fixed sizes from 9,000 to 36,000 BTU/hr. Buy the smallest standard size that covers your load; if the load exceeds 36,000 BTU/hr, split the space into two zones.
Frequently asked questions
Is my room information uploaded or saved anywhere?
No. The room size, insulation, and climate choices stay in your browser tab, and the BTU math runs there as you adjust the inputs. Nothing is sent to a server, nothing is saved on our side, and nothing is written to your browser's storage. The site sets no cookies and has no accounts; if an ad is shown, the ad network follows its own policies but still never receives your room details.
What size mini split do I need for my room?
Start from 20 BTU/hr per square foot of floor area, then adjust for ceiling height, climate, sun exposure, and insulation, add 600 BTU/hr for each person beyond the first, and add 4,000 BTU/hr if the room is a kitchen. A 500 sq ft room in a temperate climate lands near 10,000 BTU/hr, covered by a 12,000 BTU/hr (1-ton) unit.
Where does the sizing rule come from?
The core numbers follow the U.S. Department of Energy's Energy Saver guidance for sizing room air conditioners: about 20 BTU/hr per square foot, 600 BTU/hr for each person beyond the first, 4,000 BTU/hr for a kitchen, and 10% up or down for sun exposure. This calculator applies the same rule to mini-splits, adds a climate adjustment, and rounds the total up to the nearest 500 BTU/hr.
How do BTU per hour and tons relate?
One ton of cooling equals 12,000 BTU/hr. A 12,000 BTU/hr mini-split is a 1-ton unit, and 18,000 BTU/hr is 1.5 tons. The result shows the ton equivalent rounded to one decimal.
Is this estimate good enough to buy a unit?
Treat it as a starting point for ordinary rooms. Unusual layouts, large window walls, or heavy equipment can move the real load. Contractors size systems with a room-by-room ACCA Manual J load calculation, which is the professional standard, so ask for one if a quote is based on square footage alone.
What if my room needs more than 36,000 BTU/hr?
Single-zone mini-splits top out at 36,000 BTU/hr (3 tons). Above that, plan multiple zones: two or more units, each sized for its own area. Each zone then runs independently and avoids the short cycling you get from one oversized unit.