Free BTU Calculator - HVAC Sizing Made Easy
Calculate BTU requirements for heating and cooling spaces. Determine the right air conditioner, heater, or HVAC system size for your room or building.
Quick Answer
For cooling: multiply room square footage by 20 BTU. A 400 sq ft room needs approximately 8,000 BTU air conditioner.
Key Facts about BTU Calculator:
- Cooling: ~20 BTU per square foot
- 12,000 BTU = 1 ton of cooling
- Increase BTU for sunny rooms
- Oversized units waste energy
- Heating BTU depends on climate zone
Why Use Our BTU Calculator?
Complete HVAC calculations:
Cooling Calculator
AC and cooling BTU needs.
Heating Calculator
Furnace and heater sizing.
Room Adjustments
Sun, ceiling, insulation factors.
Energy Efficiency
Right-size for savings.
Instant Results
Get BTU requirements fast.
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Your data stays private.
How to BTU Calculator in 3 Easy Steps
Calculate BTU needs:
Enter Room Size
Square footage or dimensions.
Add Factors
Sun exposure, ceiling height.
Get BTU
See recommended capacity.
Size HVAC Correctly
Proper equipment sizing
Energy efficiency
Comfortable temperatures
Cost savings on equipment
Common Use Cases for BTU Calculator
Perfect for:
Frequently Asked Questions
Everything you need to know about our btu calculator
What is a BTU?
Energy unit measuring heating/cooling capacity per hour
BTU (British Thermal Unit) measures energy. One BTU heats 1 pound of water by 1°F. For AC/heating, it indicates how much heat the system can add or remove per hour.
How many BTUs do I need per square foot?
About 20 BTU per square foot for cooling
General rule: 20 BTU per square foot for cooling. A 300 sq ft room needs ~6,000 BTU. Adjust up for sunny rooms, kitchens, or high ceilings.
What size AC do I need?
300 sq ft ≈ 6,000 BTU, 500 sq ft ≈ 12,000 BTU
150-250 sq ft: 6,000 BTU. 250-400 sq ft: 8,000-10,000 BTU. 400-550 sq ft: 12,000 BTU. Add 10% for sunny rooms or kitchens.
Still have questions? Try the tool yourself!
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