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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.

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Calculate BTU

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:

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Cooling Calculator

AC and cooling BTU needs.

🔥

Heating Calculator

Furnace and heater sizing.

📐

Room Adjustments

Sun, ceiling, insulation factors.

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Energy Efficiency

Right-size for savings.

Instant Results

Get BTU requirements fast.

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100% Private

Your data stays private.

How to BTU Calculator in 3 Easy Steps

Calculate BTU needs:

1

Enter Room Size

Square footage or dimensions.

2

Add Factors

Sun exposure, ceiling height.

3

Get BTU

See recommended capacity.

Size HVAC Correctly

Proper equipment sizing

Energy efficiency

Comfortable temperatures

Cost savings on equipment

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Right Size
Efficient comfort

Common Use Cases for BTU Calculator

Perfect for:

AC Shopping

Find the right size unit.

Calculate AC Size

Heater Selection

Size furnace properly.

Calculate Heating

HVAC Planning

Full system design.

Plan System

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!

Calculate BTU

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