BTU Calculator – What Size Air Conditioner Do I Need?
Calculate the exact BTU needed for your room or home with our free AC sizing tool
AC BTU Calculator
Each person adds 600 BTU
⚡ Quick Answer
As a general rule, you need 20 BTU per square foot for moderate climates. Our calculator refines this by considering ceiling height, sun exposure, insulation, occupants, and climate zone for precise AC sizing.
Choosing the right air conditioner size is crucial for comfort and efficiency. An undersized unit won't cool effectively, while an oversized unit cycles on and off too frequently, wasting energy and failing to dehumidify. This calculator considers all factors that affect cooling requirements to recommend the perfect AC size.
Dr. Snezana Lawrence
Mathematical Historian
15+ years experience
PhD from Yale University. Published mathematical historian ensuring precision in all calculations.
Education
PhD in Mathematical History - Yale University
BTU to Room Size Chart
| Room Size | Required BTU | Tonnage |
|---|---|---|
| 100-150 sq ft | 5,000 BTU | 0.4 tons |
| 150-250 sq ft | 6,000 BTU | 0.5 tons |
| 250-350 sq ft | 8,000 BTU | 0.7 tons |
| 350-450 sq ft | 10,000 BTU | 0.8 tons |
| 450-550 sq ft | 12,000 BTU | 1 ton |
| 550-700 sq ft | 14,000 BTU | 1.2 tons |
| 700-1,000 sq ft | 18,000 BTU | 1.5 tons |
| 1,000-1,200 sq ft | 21,000 BTU | 1.75 tons |
| 1,200-1,400 sq ft | 24,000 BTU | 2 tons |
What is a BTU?
BTU (British Thermal Unit) is the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit. In air conditioning, BTU measures cooling capacity.
Higher BTU = More Cooling Power
A 12,000 BTU AC can remove 12,000 BTUs of heat per hour from your room.
Why AC Sizing Matters
❌ Too Small
- • Runs constantly
- • Never reaches desired temp
- • High energy bills
- • Shortened lifespan
⚠️ Too Large
- • Short cycles on/off
- • Doesn't dehumidify
- • Temperature swings
- • Higher upfront cost
✅ Just Right
- • Efficient operation
- • Consistent comfort
- • Proper dehumidification
- • Lower energy bills
Factors That Affect BTU Requirements
Room Size
Most important factor
Climate Zone
Hot climates need more
Sun Exposure
Sunny rooms need +20%
Insulation Quality
Poor insulation needs +30%
Ceiling Height
Tall ceilings need more
Occupants
Each person adds 600 BTU
Kitchen
Add 4,000 BTU
Electronics
Add heat load
BTU to Tons Conversion
| BTU | Tons | Typical Coverage |
|---|---|---|
| 12,000 BTU | 1 ton | 400-600 sq ft |
| 18,000 BTU | 1.5 tons | 600-900 sq ft |
| 24,000 BTU | 2 tons | 900-1,200 sq ft |
| 30,000 BTU | 2.5 tons | 1,200-1,500 sq ft |
| 36,000 BTU | 3 tons | 1,500-1,800 sq ft |
| 48,000 BTU | 4 tons | 2,000-2,400 sq ft |
| 60,000 BTU | 5 tons | 2,400-3,000 sq ft |
Frequently Asked Questions
How many BTU do I need per square foot?
General rule: 20 BTU per sq ft for moderate climates, 25-30 BTU for hot climates, 15 BTU for cold climates. Our calculator adjusts for all factors.
What happens if my AC is too big for the room?
Oversized ACs short-cycle (turn on/off frequently), fail to dehumidify properly, waste energy, and wear out faster. Proper sizing is essential.
How do I convert BTU to tons?
Divide BTU by 12,000. Example: 24,000 BTU ÷ 12,000 = 2 tons.
Does ceiling height affect BTU requirements?
Yes. Standard calculation assumes 8-foot ceilings. For 10-foot ceilings, add 25% more BTU. For 12-foot ceilings, add 50%.
Should I add extra BTU for a kitchen?
Yes, add 4,000 BTU for kitchens due to heat from appliances (stove, oven, refrigerator).
How much BTU do I need for 500 square feet?
For moderate climate: 500 × 20 = 10,000 BTU base. Adjust for sun exposure, insulation, and occupants. Typically 10,000-14,000 BTU.
Is a window unit or central AC better?
Window units work for single rooms (5,000-15,000 BTU). Central AC is better for whole homes (18,000+ BTU), more efficient, and quieter.
Can I use a portable AC instead of window unit?
Portable ACs are less efficient (need 25% more BTU for same cooling). They're convenient but cost more to operate. Window units are more efficient.
Dr. Snezana Lawrence
Mathematical Historian | PhD from Yale
Dr. Lawrence is a published mathematical historian with a PhD from Yale University. She ensures mathematical precision and accuracy in all our calculations, conversions, and academic score calculators. Her expertise spans computational mathematics and educational assessment.
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