To calculate the electricity consumption of a PC, you need to know its average power consumption at full load, the cost of electricity in your country, the number of hours of use of your desktop computer (or laptop).
Thus with the following data:
PC usage time: 8 hours,
Cost of electricity: $0,127 per KWh,
Average power consumption: 130 W.
We have 130 W per hour, 8 hours a day. That is 1040 W per day, 279.6 KW per year.
And thus $35.5 of electricity per year, $2.9 per month.
(Average power consumption in Watts x hours of use) / 1000 = total cost.
A computer consumes an average of 130 Watts (80 to 250 Watts). For advanced uses, such as intensive computing, video editing, 3D modeling, games in ultra mode, this can range from 300 Watts to 1000+ Watts (extreme cases). The same goes for servers that are very energy intensive. Daily use can also be superior, from 10 to 15 hours for those who work on their computer or are addicted to gaming.
A lot of energy is wasted when the computer or the printer are idle, unused and should instead be turned off.