BTU Calculator

Estimate the heating or cooling BTUs needed for a room.

BTU NEEDED
— BTU
heating or cooling

Usage Tip

Size your system for the hottest expected day, and remember good insulation dramatically lowers the BTUs you need.

THE MATH
BTU = Area × factor × (H ÷ 9)
Where: factor = 30/45/60 BTU per sq ft  •  H = ceiling height
• Tons = BTU ÷ 12,000  •  kW = BTU ÷ 3,412
• Add ~10% for very sunny rooms
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The calculators and tools on Formula Factory are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. Formula Factory makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.