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How Many BTUs Do You Need?
Use our free BTU calculator to quickly find out how much cooling power your space requires. Just enter your room size and a few details about your setup — no guesswork needed!
Room BTU Calculator
How to Use the BTU Calculator
Not sure where to start? Follow these simple steps to get an accurate BTU estimate for your space:
- Measure your room: Use a tape measure to find the length and width of the room. Multiply them to get the square footage (e.g., 12 ft × 15 ft = 180 sq. ft.).
- Enter your room size: Plug in the square footage where indicated in the calculator.
- Choose insulation level: If your room has good insulation and energy-efficient windows, you may need fewer BTUs. Poor insulation means you’ll need more.
- Select ceiling height: Higher ceilings mean more air to cool, which raises the BTU requirement.
- Note sun exposure: Rooms that get a lot of direct sunlight will need extra cooling power. Mark your room as “sunny” if it faces south or west or has large windows.
- Adjust for people or appliances: If the room is regularly occupied by 2+ people or has heat-generating electronics (TVs, computers), add a few hundred BTUs to the result.
- Review your results: The calculator will give you a recommended BTU range. Use this to choose the right size AC unit for your room.
Tip: It’s better to size your AC unit slightly above the minimum recommendation than to go too small. Too big, however, can lead to poor humidity control and energy waste.
What Is a BTU and Why Does It Matter?
BTU stands for British Thermal Unit, and it’s a way to measure heat. When it comes to air conditioning, it tells you how much cooling power an AC unit has. If you choose a system with too few BTUs, it won’t cool the room efficiently. Too many, and it could waste energy or cool unevenly.
What Affects the Number of BTUs You Need?
- Room Size: The bigger the room, the more BTUs required.
- Sun Exposure: Bright, sunny rooms need more cooling power.
- Insulation: Poorly insulated spaces lose cold air faster.
- Ceiling Height: Higher ceilings = more air to cool.
- Number of Occupants: More people = more body heat.
Our calculator accounts for all of these to give you an accurate estimate.
BTU Chart by Room Size
| Room Size (sq. ft.) | Recommended BTUs |
|---|---|
| 100–150 | 5,000 |
| 150–250 | 6,000 |
| 250–300 | 7,000 |
| 300–350 | 8,000 |
| 350–400 | 9,000 |
| 400–450 | 10,000 |
| 450–550 | 12,000 |
| 550–700 | 14,000 |
Frequently Asked Questions
Can I use this calculator for heating too?
While it’s primarily for cooling, the same BTU principles apply to heating — but factors like furnace type and humidity matter more for heating calculations.
What size AC unit do I need for a 12×12 room?
A 12×12 room is 144 sq. ft., which usually needs about 5,000–6,000 BTUs, depending on sunlight and insulation.
Is more BTU always better?
No. An oversized unit will cycle too quickly, failing to dehumidify the air properly and driving up energy bills.
