AC Unit Size Calculator
Find the correct air conditioner size for your space based on square footage, climate zone, and insulation quality. Get tonnage and BTU recommendations instantly.
Frequently Asked Questions
How do I calculate what size AC I need?
A common rule of thumb is 20 BTU per square foot for average conditions. Multiply your room's square footage by 20 to get base BTU, then adjust for ceiling height, insulation, sun exposure, and climate zone. Example: a 300 sq ft room needs roughly 6,000 BTU under average conditions, more in hot climates or poorly insulated rooms.
How many square feet does a 1-ton AC cool?
A 1-ton (12,000 BTU) AC unit typically cools 400–600 sq ft depending on climate, insulation, and ceiling height. In hot climates or poorly insulated spaces, coverage drops toward the lower end. In mild climates with good insulation, it can cover closer to 600 sq ft.
What size AC do I need for a 1,500 sq ft house?
A 1,500 sq ft home typically needs a 2.5 to 3-ton central AC unit (30,000–36,000 BTU), depending on climate zone, insulation quality, ceiling height, and number of windows. Homes in hotter climates or with poor insulation may need to size up.
Is it bad to oversize an AC unit?
Yes. An oversized AC cools the room quickly but shuts off before properly removing humidity, leading to a clammy feeling and higher energy bills from frequent on/off cycling (short-cycling). It's better to size accurately or slightly undersize than to oversize.
How does insulation affect AC sizing?
Poor insulation lets more heat in, increasing the cooling load — you may need 10–20% more BTU capacity than the base calculation. Good insulation, low-E windows, and shading can reduce the required tonnage. Our calculator lets you adjust for insulation quality.
What size AC do I need for a bedroom?
A typical 150–250 sq ft bedroom needs about 5,000–8,000 BTU under average conditions. Adjust upward for high ceilings, direct sun exposure, or hot climates, and downward for well-shaded, well-insulated rooms.