BTU Sizing Guide
| Room Size (sq ft) | Cooling BTU | AC Size |
|---|---|---|
| 150-250 | 5,000-6,000 | Window unit |
| 250-400 | 7,000-8,500 | Window/portable |
| 400-650 | 9,800-12,500 | Mini-split |
| 1,000-1,200 | 21,000-24,000 | 2-ton central |
| 1,500-2,000 | 30,000-36,000 | 3-ton central |
BTU Calculator
Calculate heating and cooling BTU requirements for any room based on dimensions, climate, and insulation.
📐 How We Calculate — Learn about our calculation methodology, data sources, and quality standards.
Frequently Asked Questions
What is a BTU?
British Thermal Unit — the energy needed to raise 1 pound of water by 1°F. For HVAC, BTU/hr measures heating or cooling capacity.
How many BTU per square foot?
General rule: 20-25 BTU per sq ft for cooling in moderate climates. Add 10-20% for poor insulation, heavy sun, or kitchens.
How to Use This BTU Calculator
Enter the room dimensions and insulation quality, or enter heating/cooling capacity to convert between BTU, tons, kW, and watts.
Formula & How It Works
Cooling BTU ≈ Room Area (sq ft) × 25 (base). Adjust for: ceiling height, sun exposure, insulation, climate zone, occupants. 1 ton cooling = 12,000 BTU/hr. 1 kW = 3,412 BTU/hr.
Calculation Example
Room 300 sq ft, average insulation, sunny side: 300 × 25 × 1.10 (sun) = 8,250 BTU → Choose a 10,000 BTU window unit.
Expert Tips
Oversized AC cools too quickly without dehumidifying (clammy feeling). Undersized units run constantly. Aim for the proper size per your room. Each additional person adds ~600 BTU. Kitchens add ~4,000 BTU.