AC Size Calculator
What tonnage the room actually needs — adjusted for the things that change the answer.
Recommended capacity
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- Calculated requirement
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- Smaller size viable?
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- Area per ton
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- Approx. cooling load
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Why this number
This is a rule of thumb, not a load calculation
A proper sizing accounts for wall construction, insulation, glazing and local climate — none of which a web form can know. Use this to arrive at a sensible expectation and to sanity-check what an installer proposes, particularly if they suggest something much larger.
Frequently asked
- What happens if the AC is undersized?
- It runs almost continuously without reaching the set temperature, which is both uncomfortable and expensive. An undersized unit usually costs more to run than the larger one you avoided buying, and the compressor wears faster.
- What happens if it is oversized?
- It cools quickly then shuts off, cycling on and off rapidly. That leaves the room cold but clammy, because short cycles do not run long enough to remove humidity. Oversizing is a real mistake, not a safe margin.
- Why does the top floor need more?
- A roof directly above absorbs sun all day and radiates that heat downwards. The same applies to rooms with large west-facing windows. Both add meaningfully to the cooling load.