How much electricity does a computer use?
A certified desktop computer uses **43 kWh a year**, which is about **$8**. A laptop uses 13 kWh, about $2.50. Those figures are real and measured, and for a lot of people they are also the wrong answer. The certification measures a machine that is mostly off, asleep or idling — it does not include the computer being used hard at all.
Work it out with your own tariff
Your rate, cents per kWh
There is no hours setting here, unlike the other device pages. This appliance is not certified in watts at all — only as a yearly total, and that total already includes a defined pattern of use. Multiplying it by hours of your own would count the usage twice.
| Period | Cost | Where it comes from |
|---|---|---|
| A year | $7.93 | 43 kWh — the measured figure |
| A month | $0.66 | a twelfth of the year |
| A day | $0.02 | a 365th of the year |
43 kWh × 18.44¢ = $7.93 a year. That averages 5 W drawn continuously.
43 kWh a year is the median typical energy consumption of 283 certified desktops (42.5 before rounding), measured under the ENERGY STAR procedure. Read the page before using it: that procedure weights time spent off, asleep and idling, and does not include the machine being under load at all. Rate defaults to 18.44¢ (U.S. Energy Information Administration, 2026-05) — a national average, which is wrong for you specifically, so put your own in above.
What is certified, by type
Medians from certified models, measured under the ENERGY STAR procedure.
| Type | A year | Idling | Asleep | Off | Models |
|---|---|---|---|---|---|
| Desktop | 42.5 kWh | 10.7 W | 1.6 W | 0.4 W | 283 |
| Integrated desktop | 54.1 kWh | 16.1 W | 1.9 W | 0.5 W | 122 |
| Laptop | 13.4 kWh | 4.9 W | 0.6 W | 0.3 W | 1,170 |
| Workstation | 41.0 kWh | 70.1 W | 4.3 W | 1.3 W | 70 |
The workstation row shows the problem in the data itself
Look at it again: a workstation is certified at 41 kWh a year and draws 70 watts idling. Seventy watts for a year is 614 kWh — fifteen times the certified figure.
Both numbers are correct. They are not in conflict, because the certified figure assumes the machine spends most of the year off or asleep rather than idling. That assumption is inside the measurement, and it is the reason the yearly number looks small.
Which means nobody certifies what a gaming PC uses
Under load, a desktop draws far more than it does idling, and no certification programme measures that. Not ENERGY STAR, not anybody. So when a page gives you a wattage for a gaming PC, it has either taken it from a review site's bench test of one specific machine, or made it up.
What can be done honestly is the arithmetic, with your own number in it. If you know what yours draws — a plug-in energy meter costs about the price of one of these appliances and settles it in a week — here is what four hours a day comes to:
| Draw under load | 4 h a day, a year | Cost a year |
|---|---|---|
| 150 W | 219 kWh | about $40 |
| 250 W | 365 kWh | about $67 |
| 350 W | 511 kWh | about $94 |
| 500 W | 730 kWh | about $135 |
At 350 watts — a plausible mid-range gaming machine, though not a figure we measured — four hours a day costs twelve times the certified annual total for the same computer.
The number on your power supply is not the answer either
A 750-watt power supply does not draw 750 watts. That is its maximum rated output, chosen with headroom, and a machine with one typically draws a fraction of it. Sizing a circuit from the PSU label overstates; estimating your bill from it overstates badly.
This is the same trap as the microwave, in the same direction: the largest, most visible number on the hardware is not the one you want.
Sleep costs more than you would think, and off costs almost nothing
A desktop left asleep all year, at 1.6 W, costs about $2.60 — a third of its entire certified annual figure. Fully off, at 0.4 W, it costs 65 cents.
Idling is the expensive state that people leave machines in: 10.7 W for eight hours a day is 31 kWh, about $5.80 a year, on top of everything else. If a machine is on and unattended, sleep is the setting that matters — not shutting down, which saves little more and costs you the boot.
What this does not account for
The certified figure excludes load, and that is the main thing to know. 43 kWh a year describes a machine mostly off, asleep or idling. If you use a computer hard for hours a day, the certified number is not your number and no amount of care with it will make it so.
Load is not certified by anybody. The table of load figures on this page is arithmetic on assumed draws, clearly labelled, not measurements. The only way to know your machine is to measure it at the wall.
Certified computers are a biased sample. Certification is voluntary and efficient models earn it. An older desktop, or one that was never submitted, uses more.
The monitor is not included. These figures are the computer only. A monitor adds 13 to 30 W while on — see the monitor page — and on a two-screen desk that is not a rounding error.
Workstations and gaming machines are different categories. The workstation row above is certified equipment for professional use, not a gaming PC. They are not interchangeable, and neither is certified under load.
Worth reading next
Sources
- 01ENERGY STAR certified computers V9.0 — typical energy consumption and idle powerU.S. Environmental Protection Agency ·
- 02Electric Power Monthly, Table 5.3 — average price of electricity to ultimate customersU.S. Energy Information Administration ·
How these figures are produced: see our methodology.
Figures are calculated from published wattages and a published tariff, both dated above. They are good for comparing devices, not for predicting your bill: your rate, settings and usage all differ.