Enter your heater's wattage setting, hours used, and rate to see the real cost of keeping a room warm.
Most portable space heaters run 750-1500W; the highest setting is almost always 1500W since that's the standard household circuit limit for a single plug-in appliance.
Nearly all electric space heaters are 100% resistive, meaning every watt in becomes heat out — unlike a heat pump, there's no efficiency multiplier working in your favor. Running one for a full evening every night through a winter adds up faster than most people budget for, which is worth checking against your whole-home heating cost comparison.
Because space heaters are simple resistive elements, their cost is one of the most predictable calculations in this entire toolset — no efficiency curve, no duty cycling to estimate, just wattage times hours times rate. That predictability is also why heating a whole home with space heaters instead of central heat or a heat pump is reliably one of the more expensive options available.
Only if you're heating one small room instead of a whole house — heating an entire home with multiple space heaters is almost always more expensive per BTU than central heat or a heat pump.
Most top out at 1500W (the standard 15A circuit limit), but many have lower settings around 750-900W — using the lower setting when full heat isn't needed roughly halves the running cost.
Only if it's actually rated at fewer watts — physical size doesn't reliably indicate wattage, so check the nameplate rating directly rather than assuming a compact heater draws less power.