How Many Watts Does A Laptop Use

How Many Watts does a Laptop Use? The answer to this question depends on what you mean by a “watt”. There are many ways to measure power, and different people may use the term in different ways.

First, let’s look at how manufacturers often state their products’ power consumption.  In common practice, they only list the idle and maximum power consumption of the unit as a whole, not accounting for differences within that system (as laptops have numerous subsystems which need to be considered).

You will find that most manufacturers rate their laptops between 2-3 watts while idling and around 30-35 watts when fully taxed (i.e. playing a game) – however these numbers are highly subjective because none of them take into what is actually being done with the laptop. As for the gaming pc under 700, the watts are high.

How Many Watts Does A Laptop Use

Ways Of Power Consumption In A Laptop

Manufacturers also provide the maximum power consumption, which is often listed in one of two ways: either in Volt-Amps (VA) or in It (watts).  Neither of these are accurate because they do not take into consideration the difference between voltage and current, nor Ohm’s Law.

The easiest way to calculate this number is by taking the product of Volts and Amps as opposed to multiplying volts by amps.  For example, if a laptop requires 20 Volts at 1 Amp, then it would consume 20VA/1A=20 watts.

Once you have this number for a particular system’s load (again not accounting for subsystem differences), there are several things that can be done with it.

First, you can assume that this number will stay relatively the same, regardless of what kind of battery pack is being used with it (assuming that the laptop has a fixed power supply and uses no external devices).

This means that if your laptop can run on any single voltage between 100-240 volts AC at 50-60 Hz, then its idle power consumption would be 20 watts. If you always use an external monitor with your laptop, as well as a USB hub with an external hard drive and wireless mouse and keyboard dongle, plugged into it,

then idle power consumption would be closer to 30 watts unless you disable most peripherals when not in use. Optimizing for battery life would reduce overall system load; assuming your laptop has a maximum battery life of 2 hours (this is also subjective depending on what you do with it), your laptop power consumption would be 10 watts while mobile.

How To Optimize Power In A Laptop

If, alternatively, you wanted to optimize for performance and not battery life, then the system might run at 40 watts when idling.  This number could go as high as 60 watts if an application taxed the CPU and GPU heavily enough and forced them into their respective turbo modes.

You can also compute these numbers for any given scenario using Ohm’s Law.  For example, if your laptop uses 20 volts at 1 Amp, then its resistance must be 20 ohms according to Ohm’s Law: V=IR (or Volts = Current x Resistance).  This is how we can find the power: P = V x I, and then determine that it’s dissipating 20 watts of power.

It should be noted that wattage ratings do not take into account other factors such as heat dissipation or the inefficiency of the appliances themselves.  For example, a mobile phone might have a battery with 6 watt-hours (the amount of energy it takes to run for an hour).  However, the cellphone may only hold enough charge to use 5 of those watt-hours due to inefficiencies within the system over time.

Another consideration is when discussing AC adapter specifications is their input voltage range/range from which they are regulated.  A device like this will always draw the same amount of current, but the voltage will vary with the input range.  For example, a laptop AC adapter that is rated for 100-240VAC can only deliver 20 volts DC if it’s plugged into a 240-volt outlet (and it wouldn’t even start if it were plugged into a 120-volt outlet).

CPU Power Consumption

The CPU Power tab within HWMonitor (while running a full load) shows the wattage at which your processor is consuming power.  This number will vary depending on what kind of system it’s in, as well as how many cores are being used simultaneously and their individual clock speeds.  For example, an i5-2500T has a maximum TDP of 45 watts but can go down to 35 watts with a 500 MHz decrease in frequency and disabling two of its cores.

GPU Power Consumption

The GPU Power tab within HWMonitor (while running a full load) shows the wattage at which your graphics card is consuming power.  This number will vary depending on what kind of system it’s in, as well as what kind of video chipset it has and its clock speed.  For example, an i5-2500T has a maximum TDP of 65 watts but can go down to 45 watts with a 500 MHz decrease in frequency and disabling two of its cores.

Display Power Consumption

The Display tab within HWMonitor shows the wattage at which your display is consuming power.  This number will vary depending on what kind of monitor it is, as well as its native resolution and refresh rate (or how many times per second it refreshes the image displayed).

For example, a 1080p monitor running at 60 Hz will consume less power than a 4K monitor running at 60 Hz.  The Display tab also only shows the current state of your display; if you turn your display off but leave your computer on, it will show 0 watts used even though in reality it’s drawing some small amount of power to maintain its internal state.

The Bottom Line

Wattage isn’t the most accurate method for computing power consumption or power supply specifications.  If you want to save on your electrical bill, then find out how much power each appliance uses per day and reduce it whenever possible (such as dimming lights, turning off unneeded appliances in rooms you aren’t in, and using less energy-hungry appliances).