AC BTU & Tonnage Calculator
Calculate the cooling capacity required for your space based on room dimensions and environmental factors.
How to Calculate AC Size for Your Room
Choosing the right size for an air conditioner is critical for both comfort and energy efficiency. An undersized unit will run constantly without cooling the room effectively, while an oversized unit will turn on and off too frequently (short-cycling), leading to poor dehumidification and increased wear and tear.
The Basic BTU Formula
The standard rule of thumb for residential cooling is that you need roughly 20 BTU (British Thermal Units) per square foot of living space. However, this is just a starting point. Our calculator uses a more refined algorithm that accounts for volume and environmental loads.
Step-by-Step Calculation:
- Base Area: Length × Width = Total Square Footage.
- Ceiling Height Adjustment: If your ceilings are higher than the standard 8 feet, the air volume increases, requiring more cooling power.
- Occupancy: Humans generate heat. We account for 600 BTUs for every person beyond the first two occupants.
- Sun Exposure: If the room is very sunny, capacity must increase by 10%. If it is heavily shaded, it can decrease by 10%.
- Kitchen Factor: Cooking appliances generate significant heat. If the unit is for a kitchen, an additional 4,000 BTUs is recommended.
Understanding Tonnage
In the HVAC industry, air conditioning capacity is often measured in "Tons." One ton of cooling is equivalent to 12,000 BTUs per hour. This term originates from the amount of heat required to melt one ton of ice in a 24-hour period.
Example Calculation
Imagine a living room that is 20 feet long and 20 feet wide (400 sq. ft.) with 10-foot ceilings and standard sun exposure:
- Base BTU: 400 sq. ft. × 20 = 8,000 BTU.
- Height Adjustment: (10ft / 8ft) = 1.25 multiplier. 8,000 × 1.25 = 10,000 BTU.
- If 4 people typically use the room: add 1,200 BTU (600 x 2).
- Total: 11,200 BTU (Approx 1.0 Ton unit).