How to measure your PC's power usage on Windows

Five ways to see how many watts your PC draws on Windows — what each one really measures, what it misses, and how to check your own PC in ten minutes.

The short answer: for the number your electricity bill sees, measure at the wall, with a plug-in energy meter or a smart plug that monitors energy. Software that reads your CPU and GPU sensors shows where the power goes, but it cannot see the power supply's own losses or the parts that have no sensor, so its total is always lower than the wall.

The five ways, compared

Method	What it measures	Includes PSU losses	Keeps a history	Cost
Plug-in energy meter	The whole PC, at the wall socket	Yes	Some models	Low
Smart plug with energy monitoring	The whole PC, at the wall socket	Yes	Yes, in its app	Low
Sensor software	CPU and GPU, from their own sensors	No	Depends on the tool	Free
Digital PSU telemetry	The power supply's own reading	Input reading: yes	With the vendor's software	Only if you already own one
Online PSU calculator	A theoretical maximum from a parts list	—	—	Free

Only the first two answer “what am I paying for?”. Sensor software answers “which part is drawing it?”. A PSU calculator answers a different question altogether — how big a power supply to buy — and says nothing about what your PC actually uses from hour to hour.

What Windows itself can tell you

Task Manager's Power usage and Power usage trend columns (Processes tab) rate each process from Very low to Very high. It is a ranking, not watts, and it says nothing about the PC as a whole.
powercfg /energy writes an HTML report of energy-efficiency problems — devices that block sleep, busy timers and the like. Useful for diagnosis; it contains no wattage.
powercfg /batteryreport only applies to laptops: it shows battery capacity and charge history. A desktop has no battery to report on. From version 1.0.18, PCWattVault shows the same capacity-based health live — the report's FULL CHARGE CAPACITY as a share of its DESIGN CAPACITY — plus the time left at the current draw.
A laptop running on battery is the exception: Windows knows the battery's discharge rate, which is a real measurement of the whole laptop. PCWattVault reads it on battery from version 1.0.10.

Method 1: a plug-in energy meter

Plug the meter into the wall socket and the PC into the meter. Put only the PC on it if you want the PC's figure; add the monitor and speakers if you want the whole desk. The meter reads AC power before the power supply, so it includes the supply's losses — the same thing your utility meter sees.

Read idle and load separately, and give each a minute to settle. Cheap meters are least accurate at low loads, so treat the idle reading of a very efficient PC with some caution. Most meters also count kWh: leave one in place for a day and you have your PC's real daily consumption.

Method 2: a smart plug with energy monitoring

Same measuring point as a meter, but the readings travel over Wi-Fi and the plug's app keeps a history. PCWattVault can read a TP-Link Tapo P110 or P115 directly on your own network and record your history from it — see connecting a Tapo plug in the guide.

Method 3: sensor software

Tools such as PCWattVault, LibreHardwareMonitor, HWiNFO and HWMonitor read the power sensors built into the components themselves:

CPU package power — Intel and AMD processors report their own package power. On Windows, reading it needs a kernel driver, and Microsoft Store apps may not ship one; that is why PCWattVault pairs with LibreHardwareMonitor for measured CPU values.
GPU power — NVIDIA cards report board power through the driver (nvidia-smi shows it in a terminal). AMD's Adrenalin overlay shows GPU power too; on older Radeon generations that figure covers the chip only and reads lower than the whole card draws.
What no sensor sees — the motherboard and its voltage regulators, memory on most desktop platforms, drives, fans and pumps, RGB lighting, USB devices, and the power supply's conversion losses.

To turn the sensor sum into a wall figure you need two more numbers: a base load for everything without a sensor, and your power supply's efficiency. Wall power ≈ (CPU + GPU + base load) ÷ PSU efficiency. That formula is PCWattVault's software model.

With PCWattVault, step by step:

Install PCWattVault from the Microsoft Store — it is free. GPU power is measured from the first minute.
For measured CPU power, add the free LibreHardwareMonitor: download it from its official release page on GitHub — LibreHardwareMonitor.zip suits most PCs; LibreHardwareMonitor.NET.10.zip needs Microsoft's .NET 10 runtime — unzip it, run it as administrator (accept its PawnIO driver prompt if it shows one) and enable Options → Remote Web Server; PCWattVault switches to it automatically.
Set your PSU efficiency and base load under Settings → Power model — or connect a smart plug and let the calibration button work the base load out for you.
Enter your tariff under Settings → Electricity tariff to see the result in money, live and as a permanent history.

Download LibreHardwareMonitor only from its official GitHub page. Some other websites use the LibreHardwareMonitor name without being part of the project, and what they offer may not be the genuine program. The LibreHardwareMonitor developers warn about this themselves. The same goes for the PawnIO driver: take it only from pawnio.eu or through LibreHardwareMonitor's own driver prompt.

Method 4: your power supply's own reading

Some digital power supplies report their power through the vendor's software. PCWattVault can read three families over their USB link: Corsair HXi (HX550i, HX650i, HX750i, HX850i, HX1000i, HX1200i, HX1500i), Corsair RMi (RM550i, RM650i, RM750i, RM850i, RM1000i) and MSI MEG Ai (e.g. Ai1300P). They report the power they deliver to the PC, and PCWattVault converts it to wall power using the efficiency set in Settings — it is not a wall measurement; only a plug measures at the wall. Corsair models without the “i” (RMx, RMe, HX) have no USB link and cannot be read, and NZXT power supplies are not supported. If you already own a supported one, it is a good source. Buying one only to measure is not worth it: a smart plug costs a fraction.

Why the wall reads more than the sensors

Two reasons, and neither is an error:

The power supply's losses. A PSU converts AC from the wall into DC for the components, and the difference becomes heat. An 80 PLUS Gold unit is around 90% efficient at half load, so 300 W of DC costs roughly 330 W at the wall. At idle, far below its rated load, efficiency drops and the losses become a bigger share.
Everything without a sensor. Motherboard, memory, drives, fans, pumps, lighting and USB devices typically add a few tens of watts — more on a well-equipped desktop.

An example of the arithmetic, not a measurement: the sensors report 25 W for the CPU and 20 W for the GPU at idle, and the meter shows 95 W. If the supply runs at 85% at that low load, the components are drawing about 81 W of DC — so roughly 36 W belongs to parts no sensor sees. Those 36 W are the base load.

Check your own PC in ten minutes

Put the PC, alone, on a plug-in meter or an energy-monitoring smart plug.
Open a sensor tool and find the CPU and GPU power readings.
Leave the PC idle on the desktop for two minutes, then write down the wall reading and the sensor sum.
Run a steady load for three minutes — a game, or a CPU stress test — and write both down again.
For each state, base load ≈ wall reading × PSU efficiency − sensor sum. If idle and load disagree, that is the efficiency curve at work; use the value from the state your PC spends most of its time in.
Enter the result under Settings → Power model in PCWattVault — or, with a Tapo plug connected, let the calibration bar do it in one click.

From watts to money

Energy is power multiplied by time: kWh = watts × hours ÷ 1000. A PC averaging 150 W for four hours a day uses 0.6 kWh a day — about 18 kWh a month, which at €0.25 per kWh comes to €4.50. PCWattVault does this sum continuously with your own tariff, night rates and tiers included; the user guide shows how to set it up.

FAQ

Can Task Manager show how many watts my PC uses? No. Its Power usage column rates processes from Very low to Very high relative to each other. It never shows watts, and it does not cover the PC as a whole.

Can I check it online? No — a website cannot see your PC. Online “PSU calculators” only estimate from a list of parts you type in. To know what your PC actually draws, something has to run on the PC — an app that reads its sensors — or sit at the wall: a plug-in meter or a smart plug.

Does HWiNFO or HWMonitor show my PC's total power? Not the total. They show what the component sensors report — mostly CPU and GPU. The sum is always lower than the wall reading, because the power supply's losses and the parts without sensors are missing.

Why does my smart plug read higher than the software? Because the plug measures at the wall, so it includes the power supply's losses and everything that has no sensor. The difference is expected — and it is exactly what a calibrated base load corrects.

How accurate are plug-in meters and smart plugs? Accurate enough for tracking costs: decent consumer units are typically within a few percent, and least accurate at very low loads. Neither is a certified meter — your utility's meter is.

How much power does a PC use? It varies widely. A small office PC can idle at around 20 W, while a gaming PC with a large graphics card can idle near 100 W and draw several hundred watts in a game. The only reliable figure for your own PC is a measurement.

Can I measure a laptop's power usage? Yes. On battery, Windows reports the battery's discharge rate, which covers the whole laptop, and PCWattVault reads it from version 1.0.10. From version 1.0.18 it also shows the time left at the current draw and the battery's health — the same capacity figures Windows' battery report lists, live. On the charger, measure at the wall with a meter or a smart plug. More in How much power does my laptop use?

Does PCWattVault need a smart plug? No. Without one it measures the GPU, estimates the rest — or measures the CPU too, with LibreHardwareMonitor — and marks every estimate with “~”. A plug turns the total into a real wall measurement.