AC Size Calculator — What Size Air Conditioner Do I Need?

How to Size an Air Conditioner

AC sizing starts with the cooling load — the amount of heat the unit must remove per hour. A commonly used starting point:

BTU/h ≈ Floor Area (sq ft) × 20 BTU/h

Then adjust upward for hot climates, sunny exposures and high occupancy, or downward for well-shaded, well-insulated spaces. The calculator returns the nearest standard AC size so you can match to available equipment.

Standard AC Unit Sizes (BTU/h)

• 5,000–8,000 BTU: Small rooms up to 350 sq ft (window units)
• 10,000–12,000 BTU: Medium rooms 350–550 sq ft
• 14,000–18,000 BTU: Large rooms 550–900 sq ft
• 24,000 BTU (2 tons): Up to 1,200 sq ft
• 36,000 BTU (3 tons): Up to 1,800 sq ft
• 48,000 BTU (4 tons): Up to 2,400 sq ft
• 60,000 BTU (5 tons): Up to 3,000 sq ft

Window Unit vs. Central AC vs. Mini-Split

• Window AC: Single-room cooling, 5,000–25,000 BTU, easy DIY installation, lower upfront cost
• Central AC: Whole-home cooling via ductwork, most efficient for large homes, requires professional installation
• Mini-split (ductless): Zone-based cooling without ducts, highly efficient (SEER 20+), ideal for additions and homes without existing ductwork
• Portable AC: No installation required, least efficient, good for temporary use only

Frequently Asked Questions