Baseboard Heater Sizing Calculator

About this calculator

Electric baseboard heaters are typically sized by a rule-of-thumb heat load per floor area — commonly around 10 watts per square foot for a room with standard ceiling height and insulation. That wattage then converts to BTU output via 1 W = 3.412 BTU/h, and to physical heater length using the manufacturer's watts-per-linear-foot rating (commonly 250 W/ft for standard residential units), since baseboard heaters come in fixed-length units rather than an arbitrary size.

This calculator takes a room's square footage and returns the wattage, BTU output, and linear feet of baseboard heater needed to keep it comfortable. Electricians and HVAC contractors use it when quoting a supplemental or zone-heating installation, and homeowners and renovators use it to check that a heater they're considering will actually be adequate for a bedroom, sunroom, or basement before buying it.