Find the right AC size for a room. Enter the room size, ceiling height, climate and how many people use it. The calculator estimates the cooling load in BTU and gives the nearest standard tonnage.
Rule-of-thumb estimate. An inverter AC that is slightly large usually runs better than one that is too small. For big or unusual rooms ask an HVAC engineer for a heat load calculation.
Formulas and assumptions
- Base load: floor area in square feet times BTU per square foot for your climate (30, 60 or 80), scaled by ceiling height divided by 10 feet
- People: 400 BTU for each person beyond two
- Equipment: watts of other heat sources times 3.412
- Room position: times 1.15 for top floor or sun-facing walls, times 0.9 when shaded
- Tons: BTU per hour divided by 12,000 (one ton of cooling)
Example
A 14 by 12 foot room on a top floor in a hot climate with two people has a load of about 11,592 BTU per hour, which is 0.97 ton, so a 1 ton AC fits.
Frequently asked questions
How many tons of AC do I need for my room?
In hot climates a common guide is about 1 ton for 120 to 150 square feet. This calculator adjusts for height, sun exposure, people and equipment.
What is the difference between 1 ton and 1.5 ton AC?
A 1 ton AC removes about 12,000 BTU of heat per hour and a 1.5 ton about 18,000. The bigger unit suits larger or hotter rooms.
Is a bigger AC always better?
No. A badly oversized non-inverter AC cools fast but switches on and off often, which wastes energy and removes less humidity. Pick the size closest to the load.
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