text: how much energy is my (dell) computer using in standby mode? what is the difference between stand by and off?   difference between standby and off mode:  in standby, all peripherals are switched off. that means, the modem, lan card, speakers, hard-disks, other drives... all of these are switched off. the cpu also goes into a 'low power' mode. but it does use some power.  when your computer is switched off... nothing is switched on and it uses 0 watt of power.  however, certain peripherals are also allowed to bring the computer out of standby mode (notably mouse, keyboard, and anything else that you configure in 'device manager' in windows). for such peripherals, even in standby mode they consume certain amount of power.  hope that helps, otherwise, use a watt-meter!