Some office workers leave their PC on all night
Computer magazine PC Pro measured the electricity consumed by PCs, printers and TVs.
It found many devices were extremely hungry when it comes to eating power.
But a few minor adjustments could save people hundreds of pounds.
Turn it off
A CRT (cathode ray tube) monitor left on during the day and in standby mode during the night costs an equivalent in electricity over five years as a brand new flat screen monitor, it found.
Even if you can't be bothered to save the planet, at least save yourself a few bob
Nick Ross, PC Pro Magazine
Bad practice in UK offices means many employees do not bother turning their computer off at all when they leave in the evening.
"If the screensaver is running then the monitor isn't in standby mode and it can be drawing over 100W," said PC Pro's deputy lab editor Nick Ross.
This could add up to a substantial sum when multiplied by the number of monitors in an office building.
"It would be worth many companies actually paying an employee extra to go round turning things off at the end of the day," he said.
Computers even consume electricity when they have been turned off, although a change to the settings or investing in a special power strip can cut off the entire electricity supply to the computer and its peripherals.
Saving cash
"Most people could easily save £100 a year and a small-to-medium sized company should easily cut £5,000 off its bills just by following our advice," said Mr Ross.
The picture is slightly better when it comes to TVs.
While older models can suck up 13W in standby mode, newer ones were far more environmentally friendly.
The Sony Wega widescreen and Philips flat screen TV used less than 1W when in standby, the results showed.
To highlight the issue of wasted electricity, PC Pro has launched a Switch IT Off campaign, designed to make users and manufacturers more aware of the true cost of owning electronics.
"Even if you can't be bothered to save the planet, at least save yourself a few bob," said Mr Ross.
British computer magazine ''PC Pro'' has investigated the electricity costs of running today's computers.

Their investigations showed that an individual could save £250 a year while a medium-sized business could potentially save £5,000 a year by making changes to the way computers and their peripherals are operated.

A CRT monitor uses £150 of electricity over five years; enough to pay for a new low-power LCD monitor. Using a screen saver, rather than turning the monitor off or using many computers' built-in feature to turn monitors off after a period of inactivity, could cost £100 alone in a year.

It was also discovered that turning a single laser printer off overnight and on weekends would save £70 over the life of the printer.

Many others computer users however run 'distributed computing' projects while their computers are idle, such as the '@home' series of projects (including the well-known 'SETI@home').