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Air Conditioner BTU Per Square Foot Calculator
The right AC size for any room — accounting for modern insulation.
In this article
The right size matters more than most people think
Oversized AC units cool too quickly without dehumidifying — leaving rooms cold and clammy. Undersized units run constantly without reaching target temperature. The 20 BTU/sq ft rule is a starting point; adjust for ceiling height, sun, and insulation.
Modern insulation changes everything
A well-insulated new home may need 20% fewer BTUs than an older home of the same size. If you've recently added insulation, upgraded windows, or installed weather stripping, factor this in before buying an oversized unit.
Frequently asked questions
How many BTUs do I need per square foot?▾
Standard rule: 20 BTUs per square foot. Adjust up 10–15% for full sun or poor insulation, down 10% for well-shaded modern construction.
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