What Size Space Heater Do I Need?
What wattage do you actually need?
Quick Answer
The standard guideline is 10 watts per square foot with 8-foot ceilings. A 12×10-foot room (120 sq ft) needs approximately 1,200 watts. A 15×15-foot room (225 sq ft) needs about 2,250 watts — requiring two units. Poor insulation or cold climates increase the requirement by 30–50%.
Citation-ready summary
Summary
The standard guideline is 10 watts per square foot with 8-foot ceilings. A 12×10-foot room (120 sq ft) needs approximately 1,200 watts. A 15×15-foot room (225 sq ft) needs about 2,250 watts — requiring two units. Poor insulation or cold climates increase the requirement by 30–50%.
Formula
Cost = (watts ÷ 1,000) × hours used × electricity rate per kWh.
Data used
Calculator results use user-entered wattage and usage hours, combined with residential electricity rates from the selected country or state.
Sources
Limits
These are estimates, not exact utility bills. Actual costs depend on your tariff, taxes, appliance cycling, efficiency, and how you use the appliance.