BTU Calculator
Calculate the BTUs needed for heating or cooling your room. Get accurate HVAC sizing based on room dimensions and environmental factors.
Room Size
0 BTU
0.00 tons
0.00 kW
Suggested Unit Size
5,000-6,000 BTU (Small Window Unit)
Quick Answer: BTU Guidelines
For cooling, use 20 BTU per square foot as a baseline. Adjust based on ceiling height, sun exposure, and insulation quality.
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
Table of Contents
What is a BTU?
BTU stands for British Thermal Unit. It's a measurement of thermal (heat) energy. One BTU is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.
In HVAC (heating, ventilation, and air conditioning), BTU measures the capacity of heating or cooling equipment. For air conditioners, it indicates how much heat the unit can remove from a room per hour.
Cooling (AC)
For air conditioning, BTU rating shows how much heat the unit can remove. A 10,000 BTU AC can remove 10,000 BTUs of heat per hour.
Heating
For heaters, BTU rating shows heat output. A 50,000 BTU furnace produces 50,000 BTUs of heat per hour.
BTU by Room Size Chart
Quick reference for cooling BTU requirements by room size:
| Room Size (sq ft) | BTU Needed | Room Example |
|---|---|---|
| 100-150 | 5,000 | Small bedroom |
| 150-250 | 6,000 | Bedroom |
| 250-300 | 7,000 | Large bedroom |
| 300-350 | 8,000 | Home office |
| 350-400 | 9,000 | Small living room |
| 400-450 | 10,000 | Living room |
| 450-550 | 12,000 | Large living room |
| 550-700 | 14,000 | Great room |
| 700-1000 | 18,000 | Open floor plan |
| 1000-1200 | 21,000 | Large open space |
| 1200-1400 | 23,000 | Very large space |
| 1400+ | 24,000+ | Consider multiple units |
Factors Affecting BTU Requirements
Ceiling Height
Ceilings over 8 feet need more BTUs due to larger air volume.
Sun Exposure
Rooms with lots of sun or west-facing windows need 10-15% more BTUs.
Insulation Quality
Poor insulation means more heat transfer, requiring more BTUs.
Climate Zone
Extreme hot or cold climates need additional capacity.
Occupancy
Add 600 BTU for each person beyond two occupants.
Kitchen Appliances
Kitchens need 4,000 extra BTUs for heat from cooking.
Frequently Asked Questions
How many BTUs do I need per square foot?
For cooling, you need approximately 20 BTUs per square foot. For heating, you need about 30-40 BTUs per square foot, depending on climate and insulation. These are baseline figures—adjust for factors like ceiling height and sun exposure.
What size AC do I need for a 12x12 room?
A 12x12 room (144 square feet) needs approximately 5,000-6,000 BTUs for cooling. This is a small window unit or portable AC. If the room has high ceilings or lots of sun, you may need 6,000-7,000 BTUs.
What is BTU in air conditioning?
BTU (British Thermal Unit) measures the amount of heat an AC can remove from a room per hour. A higher BTU rating means more cooling capacity. An 8,000 BTU AC removes 8,000 BTUs of heat per hour.
What happens if I get the wrong BTU size?
An undersized unit won't cool or heat effectively and will run constantly, increasing energy costs. An oversized unit will cycle on and off frequently, causing humidity problems (for AC) and uneven temperatures. It's important to get the right size.
How do I convert BTU to tons?
Divide BTU by 12,000 to get tons. One ton equals 12,000 BTU/hour. For example, 24,000 BTU = 2 tons, and 36,000 BTU = 3 tons. Central AC systems are often rated in tons.
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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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