How much electricity does a computer use?
Short answer: It depends on the machine and the workload. Apple lists the M4 Mac mini at 4 W idle and 65 W maximum, and 0.5 W asleep. At 65 W for 8 hours a day, that is about 190 kWh a year, or roughly $34 at 18¢/kWh. Light use costs a few dollars a year.
How many watts does a computer use?
A computer’s draw changes minute to minute. Idle, sleep, and full load can differ by more than 100 times. Manufacturer figures for the Mac mini show the spread.
| Mac mini configuration (Apple figures) | Idle | Maximum |
|---|---|---|
| M4, 16GB, 256GB SSD (2024) | 4 W | 65 W |
| M4 Pro, 64GB, 8TB SSD (2024) | 5 W | 140 W |
| M2, 24GB, 2TB SSD (2023) | 7 W | 50 W (CPU max) |
| M2 Pro, 32GB, 8TB SSD (2023) | 7 W | 100 W (CPU max) |
Apple’s environmental report lists the 2024 Mac mini at about 0.5 W in sleep and 0.1 W off at 115 V. The 2023 figures are labeled “CPU max,” so they may not be directly comparable to the 2024 maximums.
Larger tower PCs with separate graphics cards generally draw more. Check your own model’s spec sheet or ENERGY STAR listing for its numbers. A plug-in power meter is the most direct way to see your real draw.
Does a 750 W power supply mean my PC uses 750 W?
No. The power supply rating is the most it can deliver, not what the PC pulls. Actual draw follows the workload. A PC with a large power supply may still sit at a small fraction of that rating while browsing. Treat the rating as a ceiling, and measure if you need the real figure.
How much does it cost to run a computer?
Use this formula:
kWh per year = watts × hours per day × 365 ÷ 1,000
Cost per year = kWh × price per kWh
Example: 65 W × 8 hours × 365 ÷ 1,000 = 189.8 kWh. At 18¢/kWh, that is about $34.16 a year. The EIA expects the 2026 U.S. average residential price to be about 18.2¢/kWh.
| Scenario | kWh/year | 12¢ | 15¢ | 18¢ | 25¢ | 30¢ |
|---|---|---|---|---|---|---|
| Sleep, 0.5 W, 24 h/day | 4.4 | $0.53 | $0.66 | $0.79 | $1.09 | $1.31 |
| Idle, 4 W, 8 h/day | 11.7 | $1.40 | $1.75 | $2.10 | $2.92 | $3.50 |
| 65 W, 8 h/day | 189.8 | $22.78 | $28.47 | $34.16 | $47.45 | $56.94 |
| 140 W, 8 h/day | 408.8 | $49.06 | $61.32 | $73.58 | $102.20 | $122.64 |
| Example 300 W load, 4 h/day | 438.0 | $52.56 | $65.70 | $78.84 | $109.50 | $131.40 |
The 300 W row is a hypothetical for a heavy desktop under load, not a measured product. The 65 W and 140 W rows assume the machine runs at its stated maximum the whole time. Real daily use is usually lower. Plug your own numbers into the appliance electricity cost calculator.
Don’t forget the monitor, speakers, and other accessories. They draw power too, and some draw it when “off.” See our guide to standby power and phantom load.
Should I turn my computer off or let it sleep?
Sleep is the easy win. ENERGY STAR recommends setting the display to sleep after 15 minutes of inactivity and the computer after 30 minutes. It says power management on an ENERGY STAR certified desktop can save about $15 a year.
ENERGY STAR also notes:
- Screen savers do not save energy. Some keep the monitor drawing power.
- A game left running, even paused, can keep the computer from sleeping.
- ENERGY STAR certified computers use about 30 to 40% less energy than standard models.
Sleep at 0.5 W for 16 hours a day is about 2.9 kWh a year, roughly 53¢ at 18¢/kWh. Shutting down saves only a little more on a machine like this.
Does gaming use a lot more electricity?
Yes. Under heavy load a computer moves toward its maximum draw. Apple’s M4 Pro Mac mini maximum, 140 W, is 28 times its 5 W idle. Gaming desktops with discrete graphics cards can draw more, but figures vary widely by part. Check your card’s and system’s specs, or measure at the wall.
Consoles follow a similar pattern. See how much electricity a game console uses.
Quick answers
How many watts does a laptop or mini PC use at idle? Efficient small computers can idle in the single digits. Apple lists the M4 Mac mini at 4 W idle.
How much does it cost to leave a computer on 24/7? Multiply its average watts by 8.76 to get kWh per year. A machine averaging 65 W uses about 569 kWh, or about $102 a year at 18¢/kWh.
Does sleep mode use electricity? Yes, but very little. The 2024 Mac mini uses about 0.5 W asleep, under $1 a year at 18¢/kWh.
Do screen savers save energy? No. ENERGY STAR says a screen saver does not save energy. Set the display to sleep instead.