How to Use This Calculator
- Enter room dimensions: Measure room length, width, and ceiling height in feet.
- Select room conditions: Identify whether the room sits under an uninsulated concrete roof or catches afternoon sun.
- Purchase correct tonnage: Avoid undersizing or oversizing to achieve optimal energy efficiency and humidity control.
Formula and Calculation Steps
Base Cooling (BTU) = Floor Area (sq ft) × 65 BTU/sq ft
Roof Surcharge = +15% if Top Floor
Sunlight Surcharge = +10% if Facing Afternoon Sun
Occupants Addition = (Occupants − 2) × 500 BTU
Required Tonnage = Total BTU ÷ 12,000 (Rounded to nearest 0.5 Ton)Worked Examples and Reference Table
| Room Size | Square Footage | Middle Floor | Top Floor (Sun) |
|---|---|---|---|
| 10 ft × 12 ft | 120 sq ft | 1.0 Ton (12,000 BTU) | 1.0 – 1.5 Ton |
| 12 ft × 14 ft | 168 sq ft | 1.5 Ton (18,000 BTU) | 1.5 Ton |
| 16 ft × 18 ft | 288 sq ft | 1.5 – 2.0 Ton | 2.0 Ton (24,000 BTU) |
| 20 ft × 20 ft | 400 sq ft | 2.0 Ton | 2.5 Ton (30,000 BTU) |
Frequently Asked Questions
How do you calculate AC tonnage for a room in Pakistan?
In Pakistan's severe summer climate (temperatures often reaching 42°C to 48°C), cooling demand requires approximately 60 to 70 BTU per square foot for standard insulated rooms, plus adjustments for top floor roof heat, window sun exposure, and occupants.
How many BTU make 1 Ton of air conditioning?
One ton of refrigeration equals exactly 12,000 BTU/hr (British Thermal Units per hour). A 1.5-ton split AC provides 18,000 BTU/hr, while a 2.0-ton AC provides 24,000 BTU/hr.
Why does a top-floor room require a larger AC?
Concrete rooftops in South Asia absorb intense solar radiation throughout the day, creating thermal mass that continuously radiates heat downward into top-floor rooms, increasing cooling load by 15% to 20%.
What happens if I install an undersized AC?
An undersized AC runs continuously at maximum compressor frequency without ever reaching the set temperature. This wastes immense electricity, shortens compressor lifespan, and fails to cool during peak afternoon heat.
Are inverter ACs better for Pakistan's electricity bills?
Yes. Inverter split ACs adjust compressor motor speed dynamically rather than switching on/off abruptly, saving 30% to 50% electricity once the target temperature is stabilized.