How much does your computer cost to run?

The following equation will help work out the cost to run your computer, if, you know how many Watts it is using and how much you pay per unit of electricity:

((Watts x Hours Used) / 1000) x Cost per kilowatt-hour = Total Cost

Here in the UK at the moment we are currently charged about £0.21 per KW/h.

So, if you your computer uses 100 Watts and is on for 24 hours you would be looking at:

((100 x 24) / 1000) x £0.21 = ~ £0.50

How do I know how many Watts my computer uses?

The power consumption of a computer varies with its usage pattern.  Idle computers use less than busy computers.

If you bought a computer or laptop perhaps the manufacturer will list the power consumptions, however, if you have built the system yourself you may have to guess the consumption or get a device (ammeter) that will tell you.

Typical hardware and consumption

Normally when buying a CPU for your machine they now display the Watts it will use… many of the new dual and quad core CPUs use between 95 and 145 Watts.

Hard drives usually come in at around 5-15 Watts per drive in the system.

Mainboard can come in anywhere between 10W to 50W and RAM between 5W and 50W.

Integrated graphics cards from 3W to 15W but dedicated PCI express graphics cards anywhere between 25W to over 240+W.

Heat Generation

The more power your computer uses the more heat it will give off.  This may not be such a problem if it’s one computer you are running, however, if it’s many computers for an office or computers in a server room/data centre you may need to look at air conditioning.  Air conditioning costs money in electricity as well.

Factors that affect the amount of cooling required are:

• Size of the room
• Power consumption of computers in the room
• Lighting in the room
• Number of people in the room

With details like this you can calculate the heat/BTU generated in the room which needs cooling.

1Watt is roughly 3.412 Btu/hr, so, if you use 100 watts of power, you generate 341.2 Btu/hr.

As a rough guide (however with new cooling technologies it’s not always the case) cooling generally costs the same amount as the cost to power the machines.  There are plenty of sites online going into more technical details on howto perform all these calculations.

URLs:

HDD power:

• http://ixbtlabs.com/articles2/storage/hddpower.html
• http://www.tomshardware.com/reviews/energy-disk-drive,1944.html

Graphics cards:

• http://www.tomshardware.com/reviews/geforce-radeon-power,2122.html

General power:

• http://michaelbluejay.com/electricity/computers.html
• http://www.tomshardware.com/reviews/power-saving-guide,1611.html

Heat:

• http://en.wikipedia.org/wiki/British_thermal_unit – BTU
• http://docs.sun.com/source/816-1613-14/Chapter4.html