It turns out, there are many factors to consider when sizing a space heater.
But we’ll assume two:
Supplemental heat: The room is heated, but inadequately, so you want to boost heat by up to 10 degrees Fahrenheit.
500 watts: Up to 50 square feet (5x10, 7x7) – Bathroom, cubicle, desktop, and other personal uses
750 watts: Up to 75 square feet (7.5x10, 8x9) – Bathroom, small office, or small bedroom
1000 watts: Up to 100 square feet (10x10, 12x8) – Large bathroom, den, office, small bedroom, galley kitchen or dorm room
1500 watts: Up to 150 square feet (10x15, 12x12) – Bedroom, office, kitchen, small living room