BTU Calculator

Calculate heating and cooling BTU for any room. Supports room dimensions, area input, cooling load analysis, and energy unit conversions. Free, fast, and easy to use.

Calculate

Choose a calculation type, enter your room details or energy values, and click Calculate Now to get instant results with step-by-step solutions.

Complete User Guide

What is BTU?

BTU stands for British Thermal Unit. It is the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit. HVAC systems — heaters, air conditioners, and furnaces — are rated in BTU per hour. Knowing how many BTU your room needs helps you pick the right size system, save energy, and stay comfortable.

All Formulas at a Glance

Room Size: BTU = L × W × BTU/sq ft × Insulation × Climate

Area BTU: BTU = Area × BTU/sq ft × Insulation × Climate

Cooling Load: BTU = Base + (Windows × 1000) + (People × 400) + (Watts × 3.412)

Conversion: 1 BTU = 0.000293 kWh = 1,055 J = 252 cal

4 Calculation Types

Room Size

Enter length, width, and height to calculate BTU from full room dimensions.

Area BTU

Enter total floor area when you already know the square footage.

Cooling Load

Full cooling estimate including windows, occupants, and appliance heat.

Unit Conversion

Convert between BTU, kWh, Joules, Calories, and Foot-Pounds.

How to Use This Calculator

  1. Pick a calculation type — room size, area BTU, cooling load, or unit conversion.
  2. Enter room dimensions or area in feet or meters.
  3. Select room type, insulation quality, and climate zone.
  4. For cooling load, also enter windows, occupants, and appliance wattage.
  5. Click Calculate Now and see your BTU result with a step-by-step breakdown and chart.

BTU per Square Foot by Room Type

• Bedroom: 20 BTU/sq ft — Bathroom: 15 BTU/sq ft

• Living / Dining Room: 25 BTU/sq ft — Kitchen / Attic: 30 BTU/sq ft

• Office / Basement: 20 BTU/sq ft — Garage: 15 BTU/sq ft

Quick Examples

• 12 × 10 ft bedroom, average insulation, moderate climate → 120 sq ft × 20 × 1.2 × 1.0 = 2,880 BTU

• 200 sq ft kitchen, good insulation, cold climate → 200 × 30 × 1.0 × 1.2 = 7,200 BTU

• 1,000 BTU = 0.293 kWh = 1,055,060 Joules

Important Notes

  • These are estimates based on standard HVAC formulas. Consult a professional for exact sizing.
  • Cooling typically needs 20% more BTU than heating for the same room.
  • 1 ton of cooling equals 12,000 BTU per hour.
  • Add 10–20% extra capacity for safety margin, but avoid oversizing by more than 20%.

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