How Much Power Does a Computer Use (Sleep Mode vs Running)?

AvatarByEric Dawson Computers & Software

How much power a computer uses in sleep mode depends on its age and type, but for anything built in the last few years the answer is roughly 0.2 to 2 watts, which costs between about $0.25 and $3 a year at the June 2026 US average residential rate of 18.34 cents per kilowatt-hour. Apple’s environmental report for the M4 Pro Mac mini lists 0.5 watts asleep, and Dell’s compliance datasheet for the OptiPlex 3000 small form factor desktop lists 1.9 watts. A gaming tower with lit fans and a large power supply can pull 5 to 12 watts asleep, based on owner readings from plug-in meters. Running, those same machines draw 4 to 25 watts idling at the desktop and 65 to several hundred watts under load, so sleep cuts the overnight electricity bill by 90 percent or more compared with leaving the computer on.

How Much Power Does a Computer Use in Sleep Mode

A computer in sleep mode typically draws less than 2 watts, from about 0.2 watts on recent Apple laptops and desktops to roughly 2 watts on a mainstream Windows desktop, with gaming PCs running higher at 5 to 12 watts. Sleep, on most computers, means the processor, drives, and display are powered down while the memory stays alive so the machine can resume in a second or two. The ENERGY STAR computer specification (version 8.0, revised July 2022) defines it as a low-power mode entered automatically after inactivity, most commonly the ACPI S3 “suspend to RAM” state. Because the memory still needs a trickle of current and the power supply’s standby rail stays live, the draw never reaches zero.

Manufacturers publish the real figures in their ENERGY STAR test data, and those are far better than the guesses on most blogs. Here is what the primary sources say, as of September 2026.

Computer Sleep Idle, display on Off, still plugged in Source
MacBook Pro 14-inch, M4 (2024) 0.22 W 3.91 W 0.13 W Apple Product Environmental Report, 115 V test
Mac mini, M4 Pro (2024) 0.50 W 3.96 W 0.10 W Apple Product Environmental Report, 115 V test
Dell OptiPlex 3000 SFF, Core i5-12400 (2022) 1.91 W 23.5 W short idle, 20.7 W long idle 0.38 W Dell Product Compliance Datasheet, 230 V test
ENERGY STAR worked example, 14-inch notebook 1.0 W 10.0 W short idle, 6.0 W long idle 0.5 W ENERGY STAR Computers v8.0 specification
Home-built gaming desktops, owner meter readings 5 W to 12 W Not reported Not reported Tom’s Hardware forum thread on standby draw

Two things stand out. Apple’s laptops and small desktops sleep on well under one watt, and a mainstream business desktop from Dell lands at just under two. The gap between those and a gaming rig comes from parts that stay powered while the rest of the system is down: addressable RGB lighting, USB ports that keep charging phones, a motherboard set to wake on network traffic, and a bigger power supply whose standby circuit alone can burn a couple of watts.

Why a Laptop Sleeps on Less than a Desktop

A laptop is built around a battery, so every part of it is designed to idle as low as the engineers can manage. The 0.22 watts Apple lists for the MacBook Pro was measured with the machine plugged into its 70 watt adapter and the battery already full, so that figure includes the adapter’s own losses. Desktops have no battery to protect, and a 300 to 850 watt power supply running at one percent of its rating is not efficient. Dell’s OptiPlex 3000 uses a 300 watt unit rated 90.28 percent efficient at normal load, but at 1.9 watts most of what it draws is overhead.

Where the Old “30 Watts Asleep” Figure Comes From

You will still find guides that quote 20 or 30 watts for a sleeping computer. Virginia Cooperative Extension’s energy-estimating publication (dated February 2020, though the numbers inside it are older) lists a desktop at “120/30 or less” watts awake and asleep, and a monitor at “150/30 or less.” Those were reasonable for the tower-and-CRT era. They are not reasonable for anything sold in the last decade, and where the extension figures and the manufacturer test data disagree, the manufacturer data wins because it was measured on the specific model under a standardized ENERGY STAR test. Treat 30 watts as a ceiling for a very old machine, not a typical value.

How Much Power Does a Desktop Use When It Is Running

A desktop running at idle draws only a few watts on efficient hardware, roughly 4 to 24 watts depending on the model, and that climbs by a factor of 10 to 20 under full load such as rendering video, compiling code, or gaming.

Apple’s power-consumption support page for the Mac mini, updated November 2024, lists the M4 model at 4 watts idle and 65 watts at CPU max, and the M4 Pro at 5 watts idle and 140 watts at max. The same page shows how far things have come: the 2018 Intel Core i7 Mac mini idled at 19.9 watts and peaked at 122. Dell’s OptiPlex 3000 SFF with a Core i5-12400 measures 23.5 watts at short idle (screen on, nothing running), 20.7 watts at long idle (screen off, still awake), and 86.9 watts with the CPU stressed.

ENERGY STAR builds its annual energy rating on the assumption that a desktop spends 15 percent of the year off, 45 percent asleep, 10 percent in long idle, and 30 percent in short idle. Notebooks are weighted 25 percent off, 35 percent asleep, 10 percent long idle, and 30 percent short idle. That weighting explains why Dell’s rated annual figure for the OptiPlex 3000 is just 26.95 kilowatt-hours despite an 87 watt peak: the spec assumes the machine sleeps most of the time, which is only true if you let it.

Gaming Desktops Are a Different Category

A Berkeley Lab study by Evan Mills and Nathaniel Mills, published in the journal Energy Efficiency and summarized in a Berkeley Lab news release in August 2015, put a typical gaming computer at about 1,400 kilowatt-hours a year, six times a typical PC and 10 times a console. The graphics cards they surveyed alone ranged from 60 to 500 watts. Hardware has changed since 2015, so treat 1,400 kilowatt-hours as an order of magnitude for a machine that games daily, not a current measurement. At the June 2026 average rate that comes to roughly $257 a year, which is why sleep settings matter more on a gaming PC than on anything else in the house.

What Sleep Mode Costs per Year at the Current Electricity Rate

At the current national average rate of 18.34 cents per kilowatt-hour, sleep mode costs only a few dollars a year, about $2.05 annually for a typical office desktop left asleep overnight and roughly $1.61 a year for a low-draw machine sleeping around the clock at 1 watt. Multiply the wattage by the hours per day it runs, divide by 1,000 for daily kilowatt-hours, multiply by 365 for the year, then multiply by your rate. That is the same formula the Virginia Cooperative Extension publication gives for any household appliance.

For the rate, the US Energy Information Administration’s Electric Power Monthly, Table 5.6.A (released August 26, 2026) puts the average residential price at 18.34 cents per kilowatt-hour for June 2026, up from 17.47 cents a year earlier. Every dollar figure below uses 18.34 cents. Your own rate is on your bill, and the state figures further down show how much it moves the result.

Worked Example: One Office Desktop, Three Overnight Habits

Take the Dell OptiPlex 3000 SFF, since Dell publishes a figure for every state, and assume it is used eight hours a day and sits unused for the other 16. Over a year, the 16 idle hours cost the following, with a 27-inch Dell P2725H monitor (15.8 watts on, 0.3 watts in standby, as of September 2026) included for comparison.

Overnight habit (16 hours a day, 365 days) Watts kWh per year Cost per year at 18.34 cents
Desktop left on, screen off (long idle) 20.7 W 120.8 kWh $22.16
Desktop in sleep mode 1.9 W 11.2 kWh $2.05
Desktop shut down, still plugged in 0.38 W 2.2 kWh $0.41
Mac mini M4 Pro in sleep mode 0.5 W 2.9 kWh $0.54
Gaming desktop in sleep mode (8 W owner reading) 8 W 46.7 kWh $8.57
Monitor left on with a static screen 15.8 W 92.3 kWh $16.92
Monitor in standby 0.3 W 1.75 kWh $0.32

Sleeping the Dell instead of leaving it awake saves about $20 a year. Shutting it down instead of sleeping saves another $1.64. Leaving the monitor on all night costs more than leaving the computer on, which is the finding most people miss, and a monitor that drops into standby on its own costs almost nothing.

If you would rather work from a plain wattage, the table below converts round sleep-mode figures into a full-year cost with the machine asleep 24 hours a day, which is the worst case for a computer that is rarely used.

Sleep draw kWh per year, asleep 24/7 Cost per year at 18.34 cents
0.5 W 4.4 kWh $0.80
1 W 8.8 kWh $1.61
2 W 17.5 kWh $3.21
5 W 43.8 kWh $8.03
10 W 87.6 kWh $16.07

How Your State Changes the Math

The national average hides a four-to-one spread. In the same EIA table for June 2026, Hawaii residents paid 52.72 cents per kilowatt-hour, California 34.74, Texas 15.94, and Nevada 13.11, the lowest in the country. Run the Dell example again and the 16 hours of sleep cost $5.89 a year in Hawaii, $3.88 in California, $1.78 in Texas, and $1.47 in Nevada. Leaving the same machine awake overnight costs $63.69 in Hawaii and $15.84 in Nevada, so the savings from sleep scale with your rate while the absolute cost of sleep stays small everywhere.

Sleep, Hibernate, or Shut Down: Which One Uses the Least Power

Hibernate and shutdown use the least power of the three, with sleep drawing a bit more to keep the memory refreshed, according to Microsoft’s support page comparing the options. Shutting down turns the machine off completely. In wattage terms, hibernate and shutdown are the same thing, the 0.1 to 0.4 watt standby figure in the tables above, and sleep sits a little higher.

On the Apple side, the environmental reports note that a Mac sleeps automatically after 10 minutes of inactivity by default, and the sleep figures were measured with “Wake for network access” turned on and an Ethernet cable connected. In other words, Apple’s 0.5 watt number already includes the cost of staying reachable on the network.

Modern Standby Versus S3 on Windows

Many Windows laptops and some desktops sold since 2020 no longer use classic S3 sleep. Microsoft’s hardware documentation explains that Modern Standby keeps the system in the S0 running state with the screen off and powers components down one by one, which makes resume at least twice as fast as S3 but allows approved background work to continue. The same document says a Modern Standby system on AC power can enter maintenance mode, install updates, and use the network while it appears to be asleep. That is why a “sleeping” desktop sometimes spins its fans at 2 a.m., and why a Modern Standby machine can average more than the 1 to 2 watts a true S3 sleep would draw.

ENERGY STAR sets a ceiling for this behavior. To claim “full network connectivity” while asleep, a computer must hold its network presence at 10 watts or less, and the desktop proxy allowances in the specification reward machines that do it at 2.5 or 3 watts. Any computer drawing more than 10 watts asleep is behaving worse than the certification allows.

How Many Amps Does a Computer Monitor Use

A typical computer monitor draws well under an amp, roughly 0.1 to 0.6 amps depending on brightness and load, since amps equal watts divided by the 120 volts a US outlet supplies. Dell’s specification for the P2725H, a 27-inch 1080p business monitor, lists 15.8 watts in typical use, 74 watts maximum at full brightness with every port loaded, and 0.3 watts in standby. Divide by 120 and that is 0.13 amps typical, 0.62 amps at the absolute maximum, and a few thousandths of an amp asleep.

The label on the back of that same monitor says 1.5 amps. Nameplate ratings are worst-case numbers written for the whole 100 to 240 volt range the supply accepts, and they exist so an electrician can size a circuit, not to tell you what the screen consumes. Bigger and brighter panels draw more when on, so check the On mode figure in your own monitor’s specifications; the standby figure will almost always be a fraction of a watt, like the Dell’s.

For the computer itself, the same division applies. Dell’s 86.9 watt CPU-stressed reading is 0.72 amps, a gaming rig pulling 300 watts is 2.5 amps, and a 500 watt peak is about 4.2 amps. A standard 15 amp household circuit therefore has room for a high-end PC, two monitors, and a desk lamp with margin to spare, though a plug-in meter will read slightly more current than this arithmetic suggests because switching power supplies do not draw a perfect sine wave.

How to Measure What Your Own Computer Really Draws

The only way to know what your own computer really draws is to measure it at the wall, since published figures cover only the exact configuration the manufacturer tested and your machine likely has different memory, drives, peripherals, and settings. A plug-in energy meter, the kind sold under names like Kill A Watt, sits between the outlet and the computer and reads watts in real time. The Tom’s Hardware thread cited above has owners reporting 5 watts and 8 to 12 watts asleep from exactly this kind of meter, and one contributor cautions that accuracy falls off below a few watts, so read a sleeping computer’s draw as “about 2” rather than “1.7.”

Without a meter, the Virginia Cooperative Extension guide suggests reading the nameplate wattage or multiplying the nameplate amps by 120, but as the monitor example shows, that gives you a maximum, not an average. A meter costs less than one year of a gaming PC’s overnight idle, so it pays for itself quickly if the readings change a habit.

If Your Computer Still Draws Too Much Asleep

A sleeping desktop that reads 15 watts or more, or a shut-down machine reading anything above about one watt, has something wrong. Work through these in order.

  1. Confirm it is actually asleep. On Windows 11 the machine should show no display signal and a slow-blinking power light. A screen that is merely off with the system awake is long idle, which on the Dell example is 20 watts, not 2.
  2. Turn off lighting and USB charging. RGB strips and powered USB ports stay live in S3 sleep on many motherboards. The option is usually called ErP, “ErP Ready,” or “Power On By USB” in the motherboard firmware, and enabling ErP disables both.
  3. Check Wake on LAN and network presence. A network card that stays awake to listen for packets is a small but constant load. Disable “Wake on Magic Packet” in the adapter’s Advanced properties in Device Manager if you never wake the PC remotely.
  4. Look for Modern Standby maintenance. If the machine wakes itself for updates, running powercfg /a in a Command Prompt shows which standby model it uses. A desktop that supports S3 can often be switched back to it in firmware, and that stops background maintenance from running while it appears asleep.
  5. Suspect the power supply. In the Tom’s Hardware thread, one owner measured 50 watts with the PC shut down and every cable except the mains disconnected, and a replacement of the same model did the same. Replies called 5 to 15 watts the normal standby range for a whole PC and blamed a faulty standby circuit. If the reading persists with nothing but the power supply connected, the supply is the problem.
  6. Use the switch. Most ATX supplies have a rocker switch on the back. Flipping it, or using a switched power strip, takes the whole system to zero, at the cost of losing sleep entirely and needing a full boot.

How to Make Your Computer Sleep Sooner

To make your computer sleep sooner, lower the sleep and screen-off timers below the ENERGY STAR default, which requires a 15-minute display timeout and a 30-minute system timeout and is estimated to save about $15 a year for a desktop. Manufacturers and users change them all the time, so it is worth checking.

On Windows 11, Microsoft’s power settings page gives the path as Settings, then System, then Power & battery, then “Screen, sleep, & hibernate timeouts.” Two dropdowns matter: “Turn my screen off after” and “Make my device sleep after,” each with a separate value for plugged in and on battery. Under the same Power & battery heading, Power Mode offers “Best Power Efficiency,” which Microsoft describes as reducing consumption by limiting background activity. To add hibernate to the power menu on a desktop where it is hidden, Microsoft’s instructions are Settings, System, Power & sleep, Additional power settings, “Choose what the power button does,” then “Change settings that are currently unavailable,” and tick Hibernate under Shutdown settings.

For a Mac, the defaults already sleep the system after 10 minutes, according to Apple’s environmental reports, and the sleep draw is low enough that there is little to gain from tuning further. The one setting worth knowing is “Wake for network access” in the Energy settings, which keeps the Mac reachable at a fraction of a watt; turning it off saves almost nothing on an Apple silicon machine.

Whatever the platform, the monitor deserves its own attention. The Dell figures above show a screen left on all night costs more than the computer it is attached to, and a monitor only enters its 0.3 watt standby when the computer stops sending it a signal, so the “Turn my screen off after” timer is the single setting with the largest payoff.

Frequently Asked Questions

Does a Computer Use Electricity When It Is Turned off but Still Plugged In?

Yes, a small amount. Apple measures the shut-down Mac mini at 0.10 watts and the MacBook Pro at 0.13 watts, and Dell measures the OptiPlex 3000 at 0.38 watts. Even at Hawaii’s rate, 0.38 watts around the clock is under $2 a year, so unplugging is a matter of tidiness rather than savings.

Does a Laptop Charger Use Power with Nothing Connected?

A little. Apple’s report for the MacBook Pro 14-inch lists the 70 watt USB-C adapter at 0.05 watts with no load at 115 volts, which is about 0.4 kilowatt-hours a year, or eight cents. Older or cheaper adapters can be worse, and a warm brick with nothing attached is the sign to unplug it.

How Much Does It Cost to Run a Computer 24 Hours a Day?

Depends entirely on what it is doing. A Mac mini M4 Pro idling at the desktop with the display on uses about 34.7 kilowatt-hours a year, or $6.36 at 18.34 cents, while the Dell OptiPlex 3000 at short idle uses 206 kilowatt-hours, or $37.83. Match the Berkeley Lab average of 1,400 kilowatt-hours with a gaming machine and the bill is about $257 a year.

Does a Monitor Go to Sleep When the Computer Does?

Normally yes. When the computer sleeps or turns its display output off, the monitor loses signal and drops into standby on its own, which on the Dell P2725H means 0.3 watts. A monitor that stays lit with a “no signal” message for hours is usually one with its own power-saving option turned off in its on-screen menu.

Put a plug-in meter on the computer once, note the sleep and idle readings, and set the screen to turn off after 10 minutes and the system to sleep within 30. On the manufacturer figures above, that habit turns a $20 to $40 a year overnight cost into $2 or less, and the meter will show within a week whether your machine also needs its lighting and USB power switched off.

References

  • Table 5.6.A. Average Price of Electricity to Ultimate Customers by End-Use Sector, by State, June 2026 and 2025, U.S. Energy Information Administration, read September 2026
  • ENERGY STAR Program Requirements for Computers, Version 8.0 (Rev. July 2022), ENERGY STAR, read September 2026
  • Computers, ENERGY STAR, read September 2026
  • Mac mini Product Environmental Report, October 2024, Apple, read September 2026
  • MacBook Pro 14-inch Product Environmental Report, October 2024, Apple, read September 2026
  • Mac mini power consumption and thermal output (BTU) information, Apple Support, read September 2026
  • OptiPlex 3000 SFF Product Compliance Datasheet, Dell, read September 2026
  • Dell Pro 27 Plus Monitor P2725H, Dell, read September 2026
  • Shut down, sleep, or hibernate your PC, Microsoft Support, read September 2026
  • Power settings in Windows 11, Microsoft Support, read September 2026
  • Modern Standby vs S3, Microsoft Learn, read September 2026
  • Gaming Computers Offer Huge, Untapped Energy Savings Potential, Berkeley Lab News Center, read September 2026
  • ENERGY SERIES: Estimating Appliance and Home Electronic Energy Use, Virginia Cooperative Extension, read September 2026
  • PSU Standby consumption, Tom’s Hardware Forum, read September 2026

Author Profile

Eric Dawson
Eric Dawson
Eric Dawson is the writer and curious mind behind The Money Watch. Based in Columbus, Ohio, he has a habit of digging into everyday questions until he understands what is actually going on, whether the subject is technology, travel, shopping, food, business, consumer products, or one of life's oddly specific problems.

Rather than pretending to be an expert in everything he covers, Eric approaches each topic as a careful researcher and practical problem-solver. He favors original sources, clear explanations, and honest answers about uncertainty. His goal is simple: do the digging readers shouldn't have to do themselves and turn what he finds into useful information without wasting their time.