Room Heater Size Calculator

Find the right wattage space heater for a room.

HEATER WATTAGE
W
recommended

Usage Tip

Most space heaters max out at 1,500 W on a standard 15A outlet, good for rooms up to ~150 sq ft.

THE MATH
Watts = Area × W/sq ft
Where: W/sq ft = 8/10/12 by insulation quality
• Amps = Watts ÷ 120V
• BTU/hr = Watts × 3.412
Scroll to Top

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.