BTU Calculator – What Size Air Conditioner Do I Need?
Calculate the BTU air conditioning capacity you need for any room. Based on room size, ceiling height, sun exposure, and number of occupants. Find your ideal AC unit size.
☃️ Home📐 BTUs = Room Area × 25 (adjusted for height, sun & occupants)
Room length (feet)
Room width (feet)
Ceiling height (feet)
Number of people usually in room
Sun exposure
Room type
Please enter valid values.
Formula & Reference
| Variable | Formula | Units |
|---|---|---|
| BTU Calculator – What Size Air Conditioner Do I Need? | BTUs = Room Area × 25 (adjusted for height, sun & occupants) | BTU/hr |
Step-by-Step Examples
Example 1
Standard Bedroom
12×15 ft, 8ft ceiling, 2 people, normal sun.
- Area: 180 sq ft | Base: 4,500 BTUs
- Adjusted: ~5,700 BTUs | Recommend: 6,000 BTU window unit
✓ ~6,000 BTU unit
Example 2
Sunny Living Room
20×25 ft, 9ft ceiling, 3 people, sunny.
- Area: 500 sq ft | Adjusted: ~14,900 BTUs
- Recommend: 18,000 BTU mini-split
✓ ~18,000 BTU mini-split
Example 3
Kitchen
12×14 ft, 8ft ceiling.
- Area: 168 sq ft + 4,000 BTU kitchen bonus
- = ~8,200 BTUs | Recommend: 8,500 BTU unit
✓ ~8,500 BTU unit
Real-World Applications
Homeowners
Buy the right size AC unit the first time.
HVAC Shoppers
Compare window units and mini-splits by BTU.
Contractors
Quick BTU estimate during site visits.
Property Managers
Specify correct AC size for rental units.
Common Mistakes to Avoid
⚠️
Bigger isn't better for AC
Oversized AC cools the room too quickly without removing humidity. This causes a cold, clammy feeling and higher energy costs. Always size correctly.
⚠️
Not accounting for kitchen heat
Kitchens require an additional 4,000 BTUs beyond the room-size estimate due to cooking heat and appliances.
Frequently Asked Questions
How many BTUs per square foot? ▾
The general rule is 20-25 BTUs per square foot. Adjust up for kitchens, sunny rooms, or high ceilings. Adjust down for shaded or well-insulated rooms.
What does 1 ton of AC mean? ▾
1 ton = 12,000 BTU/hr. This dates from the days when ice was used for cooling (1 ton of ice = 12,000 BTUs of cooling per hour). Window units are typically 0.5-2 tons; central AC is 1.5-5 tons.
Window unit vs mini-split vs central AC? ▾
Window unit: cheap ($150-500), easy to install, cools one room. Mini-split: $700-3,000, no ductwork, highly efficient, cools multiple zones. Central AC: $3,000-10,000+, cools whole house.
How often should I replace my AC? ▾
Window units: 10-15 years. Mini-splits: 15-20 years. Central AC: 15-20 years. Replacing a 15+ year old unit with a modern high-SEER unit typically saves 20-40% on cooling costs.