AC Sizing Calculator
Get the right-sized air conditioner in seconds. Enter your room details and receive an accurate BTU/h and tonnage recommendation — free, no sign-up required.
How AC Sizing Works
Our calculator uses a simplified Manual J methodology — the same approach HVAC engineers use — to estimate the total cooling load for your space.
Enter Room Details
Input dimensions, windows, glazing type, shading, and occupancy. Switch seamlessly between feet / m² units.
Set Climate & Region
Pick US, EU, Scandinavia, or UAE — or enter a custom outdoor design temperature and humidity level for precise results.
Get Your Recommendation
Receive instant results in BTU/h, tons (US), and kW — with a full breakdown: transmission, solar, internal gains, and latent load.
AC Sizing Calculator
Manual J simplified methodology
Longest wall of the room
Shorter wall of the room
Floor to ceiling
How to Use the AC Sizing Calculator
How to Use the AC Sizing Calculator
- 1
Select Region and Units
Choose your market region (United States, Europe, Scandinavia, or UAE) to automatically switch between imperial and metric units and pre-fill design temperatures appropriate for your climate.
- 2
Enter Room Dimensions
Input the room length, width, and ceiling height. Use the sliders or type the values directly. Select your insulation quality — this significantly affects the calculated heat load.
- 3
Add Windows and Occupancy
Add each window with its dimensions, orientation, glazing type, and shading. Then enter the number of occupants, equipment wattage, and lighting wattage for the space.
- 4
Set Design Temperatures
Adjust the outdoor design temperature to the hottest expected summer temperature in your area, and set your desired indoor temperature. Higher temperature differences increase the calculated load.
- 5
Review Results and Recommendations
The calculator shows your total cooling load in BTU/h (or W), the recommended AC capacity, and a breakdown of heat sources. Use the product suggestions to find a unit matching your requirements.
Pro Tip: Use Ctrl+Enter to calculate quickly, or Ctrl+R to reset the form.
Frequently Asked Questions
How many BTUs do I need for my room?
A rule of thumb is 20 BTU/h per sq ft, but accurate sizing depends on insulation, window area and orientation, occupancy, internal heat sources, and outdoor design temperature. Our calculator accounts for all these factors plus a built-in 15% safety factor to cover peak summer loads.
What's the difference between BTU/h, kW, and tons?
All three measure cooling capacity. 1 ton of refrigeration = 12,000 BTU/h ≈ 3.517 kW. BTU/h is the US standard, kW is used in Europe and internationally, and tons are common with HVAC professionals in North America. The calculator shows all three units simultaneously.
Why does humidity increase the required cooling capacity?
AC units remove both sensible heat (temperature) and latent heat (moisture). High humidity means a greater dehumidification load. We apply a ×1.15 multiplier for average humidity and ×1.30 for humid climates like the UAE or coastal areas — humidity is set automatically per region.
Should I buy a larger AC unit for extra safety?
No — oversizing is one of the most common and costly mistakes. An oversized unit short-cycles (brief cooling bursts), which prevents proper dehumidification, causes temperature swings, increases mechanical wear, and wastes electricity. Our calculator already includes a 15% safety margin — that is sufficient.
How do I choose the right insulation setting?
Select 'Poor' (U=1.8 W/m²K) for older homes without wall insulation. Choose 'Average' (U=1.2 W/m²K) for standard modern construction. Use 'Well Insulated' (U=0.6 W/m²K) for passive-house standard or recently retrofitted buildings. When unsure, 'Average' is a safe default for most residential properties.
How much do windows affect the cooling load?
Significantly — south and west-facing windows in summer receive direct solar radiation that can add 200–500 W per m² to the cooling load. Shading (blinds, external overhangs) reduces solar gains by 50–70%. In Step 2 you can configure each window's orientation, glazing type, and shading level individually for precise solar load calculations.
trustpilot.message