A desktop computer typically draws 100 to 800 watts while running, depending on the processor, graphics card, and what you are doing. A laptop uses 20 to 100 watts. The actual cost to your electric bill depends on your local electricity rate, how many hours per day the machine runs, and whether it idles or works at full load.

Most people overestimate computer power use because they confuse peak wattage with average draw. A gaming desktop might have a 750-watt power supply, but that does not mean it pulls 750 watts all day. Checking your actual consumption takes a few minutes and costs nothing.

Key Takeaways

  • A desktop computer draws between 100 and 800 watts depending on its components, while a laptop draws 20 to 100 watts.
  • You can measure your computer's real power draw with a plug-in watt meter, which costs $15 to $30 and shows live consumption.
  • Idle power use — what your computer draws when you are not actively using it — is often 30 to 50 percent of total daily consumption.
  • Turning off your monitor saves more electricity than turning off the computer itself, since monitors can draw 30 to 60 watts continuously.
  • The annual cost to run a typical desktop eight hours a day is roughly $50 to $150, depending on your local electricity rate and the machine's efficiency.

What determines how much power your computer uses

The main factors are the processor, graphics card, and power supply size. A modern Intel Core i5 or AMD Ryzen 5 processor draws 65 to 125 watts under load. A dedicated graphics card — especially a gaming GPU — can add 150 to 450 watts. A basic integrated graphics chip adds almost nothing.

The power supply itself is rated higher than the system will ever draw, so a 750-watt supply does not mean the computer uses 750 watts. The supply is sized to handle peak demand plus headroom. A typical office desktop with a mid-range processor and no dedicated GPU draws 150 to 300 watts under full load.

What the computer is doing matters too. Browsing the web or editing a document uses far less power than gaming or video rendering. During idle — when the machine is on but you are not using it — power draw drops to 30 to 100 watts depending on the system.

How to measure your computer's actual power use

The most direct method is a plug-in watt meter, also called a power meter or kill-a-watt meter. You plug the meter into the wall outlet, plug your computer into the meter, and it displays live wattage and cumulative kilowatt-hours. Models from brands like Killawatt or P3 cost $15 to $30 and work with any device.

Leave the meter connected for a full day of your normal use — work, browsing, idle time, and shutdown. Record the kilowatt-hours shown at the start and end of the day. The difference is your daily consumption. Multiply that by 365 to get annual use, then multiply by your local electricity rate (usually $0.10 to $0.20 per kilowatt-hour, but varies by region and season).

If you want a quicker estimate without buying a meter, check your computer's power supply label. It shows the maximum wattage. Assume the system draws 50 to 70 percent of that rating during typical use and 10 to 20 percent while idle. This is rough but gives you a ballpark figure.

Desktop versus laptop power consumption

Laptops are designed to run on battery, so they use far less power than desktops. A typical laptop draws 20 to 60 watts while working and 5 to 15 watts while idle or sleeping. Even a high-performance gaming laptop rarely exceeds 100 watts.

A desktop uses more power because it does not need to fit in a small case or run on battery. The trade-off is that a desktop can deliver more processing power for the same cost. If you run a desktop eight hours a day, it costs roughly $50 to $150 per year in electricity. A laptop running the same hours costs $10 to $40 per year.

If you work from home and have a choice, a laptop saves money on electricity. If you need the performance a desktop offers, the electricity cost is usually small compared to the hardware cost and the work you do with it.

Why idle power use matters more than you think

Many people leave their computer on all day, even when they step away for hours. During those idle periods, the machine still draws 30 to 100 watts — less than under load, but steady. If your computer idles for 16 hours a day and works hard for 8 hours, idle time may account for 40 to 50 percent of your total daily power use.

Putting the computer to sleep or hibernation cuts idle power to near zero — usually under 5 watts. The tradeoff is a 10 to 30 second wake-up delay. For most people, this is worth it. If you step away for more than 30 minutes, sleep mode saves money and reduces wear on the hardware.

Monitors are often forgotten in this calculation. A typical LCD monitor draws 30 to 60 watts while on and nearly zero while off. If you leave your monitor running while your computer sleeps, you are wasting as much power as the computer itself. Turning off the monitor when you step away is one of the fastest ways to cut electricity use.

Estimating your annual electricity cost

Start with your daily kilowatt-hour use (measured with a watt meter or estimated from the power supply rating). Multiply by 365 to get annual kilowatt-hours. Then multiply by your local electricity rate.

Example: A desktop that draws an average of 200 watts (0.2 kilowatts) running 8 hours per day uses 1.6 kilowatt-hours per day, or 584 kilowatt-hours per year. At $0.13 per kilowatt-hour (a typical U.S. rate), that is about $76 per year. At $0.20 per kilowatt-hour (higher in some states), it is $117 per year.

Your local rate appears on your electric bill. Rates vary by state, season, and time of day. Some utilities charge more during peak hours (usually afternoon and evening). If your computer runs mostly during off-peak hours, your actual cost may be lower.

Ways to reduce computer power consumption

Enable sleep mode in your operating system settings. Windows and macOS both let you set the computer to sleep after a period of inactivity — typically 10 to 30 minutes. This cuts idle power use to nearly zero without shutting down.

Turn off the monitor separately from the computer. Many monitors have a power button; use it when you step away. Some monitors also have a built-in sleep mode that activates after a set time.

Unplug peripherals you do not use daily. External hard drives, printers, and USB hubs draw small amounts of power even when idle. If you use them once a week, unplug them the rest of the time.

Use a power strip with an on-off switch for your entire setup. This lets you cut power to the computer, monitor, and peripherals all at once without unplugging individual cables. Some smart power strips cut power to devices that are off, saving the phantom power draw.

Upgrade to a more efficient power supply if your desktop is old. Older power supplies waste 20 to 30 percent of the electricity they draw as heat. Modern 80+ Bronze or better supplies waste only 10 to 15 percent. The savings add up over several years, though the upfront cost is $50 to $150.

Frequently Asked Questions

Does leaving a computer on all the time cost a lot more than turning it off?

Yes. A desktop left on 24 hours a day uses roughly three times as much electricity as one used 8 hours a day. If you are away for more than an hour, sleep mode costs almost nothing and wakes in seconds. Shutdown costs more in wear on the hardware but saves the most electricity if you are gone for 8+ hours.

How much does it cost to run a gaming PC?

A gaming desktop with a high-end graphics card can draw 400 to 800 watts under load. If you game 4 hours a day and idle the rest, expect $100 to $250 per year in electricity, depending on your local rate and the exact components. Turning off the monitor when not gaming cuts this by 20 to 30 percent.

Is it bad to leave a computer on sleep mode overnight?

No. Sleep mode draws 1 to 5 watts, which is negligible. Waking from sleep is when ready or near-when ready. Hibernation uses even less power but takes longer to wake. Both are safe for the hardware and save far more electricity than leaving the computer fully on.

Can I tell how much power my computer uses without a watt meter?

You can estimate using the power supply wattage and assuming 50 to 70 percent average load, but this is rough. A watt meter gives you the real number and costs $15 to $30. If you plan to reduce power use, a meter shows you which changes actually save money.

Does unplugging a computer save electricity compared to turning it off?

Turning it off cuts power use to near zero. Unplugging saves the same amount of electricity but also prevents phantom power draw from the power supply itself, which is usually under 1 watt. For most people, turning off is enough; unplugging is only necessary if you want to eliminate every last watt.