That is a good question that is not so easily answered by these specs. First thing is there is a difference between "MAXIMUM" or running wattage, versus STARTUP or SURGE wattage. This unit says it uses 900 or so Watts Maximum, but that does not tell you how many watts the unit uses to initially start the compressor. This number is always higher than that Maximum running watts. This could be 2 to 3 times higher than that the maximum running watts. So this 900W max unit could use say 1500-2500 watts or more to start the compressor then level off at 900watts once it's going, for example. So do your homework!