Air Conditioner Size Calculator
Estimate the recommended AC cooling capacity in BTU/hr, tons, and kW using room size, ceiling height, sunlight, insulation, climate, occupants, and heat load.
Results
This is a planning estimate. Real AC sizing can vary by insulation, window direction, air leakage, ceiling height, local climate, humidity, equipment heat, occupancy, duct design, and room layout. For central HVAC or whole-home systems, use a professional Manual J style load calculation.
Use this Air Conditioner Size Calculator to estimate the cooling capacity needed for a room in BTU/hr, tons, and kW. The estimate considers room dimensions, ceiling height, sunlight, insulation, climate, occupants, and additional heat sources.
AC Sizing Method
Room area = length × width
The calculator estimates a base cooling load from the room size and then adjusts the result for factors that can increase or reduce cooling demand, including:
- Ceiling height
- Sun exposure
- Insulation quality
- Local climate
- Number of occupants
- Kitchen or equipment heat
- Extra capacity margin
For comparison, ENERGY STAR recommends sizing room air conditioners primarily by floor area and then adjusting for conditions such as heavy shade, strong sunlight, additional occupants, and kitchens.
Useful capacity conversions are:
1 cooling ton = 12,000 BTU/hr
1 kW of cooling ≈ 3,412 BTU/hr
Example
Suppose a room measures 20 ft by 15 ft.
Room area = 20 × 15 = 300 ft²
ENERGY STAR’s room-air-conditioner sizing guidance recommends approximately 8,000 BTU/hr for an area of 300 to 350 ft² under standard conditions.
The required capacity may increase if the room has high ceilings, strong sunlight, poor insulation, a hot climate, several occupants, or significant equipment heat.
Important Notes
- A larger air conditioner is not always better. Oversized units can cool too quickly without removing enough humidity.
- Room shape, windows, air leakage, orientation, humidity, insulation, and internal heat sources can significantly affect cooling load.
- This calculator provides a planning estimate rather than a complete HVAC design calculation.
- For central air conditioning, whole-home systems, major renovations, or equipment replacement, use a professional residential cooling-load calculation such as ACCA Manual J.