AC Tonnage Calculator

Understanding AC Tonnage

AC tonnage is a measure of cooling capacity derived from the historical practice of using ice for cooling. One ton of cooling equals 12,000 BTU per hour—the amount of heat absorbed when one ton (2,000 lbs) of ice melts over a 24-hour period. Understanding tonnage is essential for selecting the right air conditioner for your space.

BTU to Tonnage Conversion

Converting between BTU and tonnage is straightforward:

• To get tons from BTU: Divide BTU by 12,000
• To get BTU from tons: Multiply tons by 12,000
• Example: 18,000 BTU ÷ 12,000 = 1.5 tons

Common AC Tonnage and Their Applications

Standard residential AC sizes include:

• 0.75 Ton (9,000 BTU): Small bedrooms, 80-120 sq ft
• 1.0 Ton (12,000 BTU): Regular bedrooms, 100-150 sq ft
• 1.5 Ton (18,000 BTU): Large bedrooms/offices, 150-250 sq ft
• 2.0 Ton (24,000 BTU): Living rooms, 250-350 sq ft
• 2.5 Ton (30,000 BTU): Large living areas, 350-450 sq ft
• 3.0 Ton (36,000 BTU): Commercial spaces, 450-550 sq ft

Factors Affecting Tonnage Requirements

The right tonnage depends on more than just square footage:

• Ceiling height: Add 15% for each foot above 8 ft
• Sun exposure: South/West facing rooms need 10-15% more
• Insulation quality: Poor insulation adds 20-30%
• Occupancy: Each person adds 600 BTU load
• Kitchen/equipment: Add 10-20% for heat-generating areas

Why Right-Sizing Matters

Selecting the correct tonnage is crucial for efficiency, comfort, and equipment longevity. An undersized AC runs continuously without reaching the setpoint, while an oversized unit short-cycles, fails to dehumidify properly, and wastes energy through frequent startups.