How To Calculate Watts a Laptop Use: End-to-End Guide

No single answer to the question. BUT there are just 2 simple steps to find watts your laptop uses. Bonus: illustrative example, find how long the battery will last and how to make it last longer.

Once you bought a gaming laptop, laptop for business or studying, it is important to get to know how many watts it consumes, why? Having this number you will be able to calculate how long the battery will last without a power supply. It will be helpful to know if you plan to use the laptop during travels or outside the home.

How to find how many watts a laptop uses?

From the laptop label

You can easily find how many watts a laptop uses by taking a look at the power adapter from your laptop or find it on the laptop casing.

The number with a “W” will show how many watts your laptop uses.

Dell laptop’s power adapter

Calculate how many watts a laptop use

If you cannot find a number with “W” at the power adapter or laptop casing, then you need just to calculate the watts. It is extremely easy:

  1. Use numbers from the “output” line — Voltage (V) and Amperes (A);
  2. Multiply them and you get watts.

Let’s take as an example number from this power adapter:

19.5 V * 4.62 A = 90 W

Dell laptop’s power adapter

How to calculate how long the laptop’s battery will last?

Besides, the number of watts your laptop uses, you will need Voltage (V) and Milliamp Hours (mAh) from the laptop’s battery. If the battery is removable, you will find them on it; if it isn’t — then on the laptop casing.

Now, when you have all the necessary numbers (Watts, Voltage, and Milliamp Hours), you can calculate how long your laptop will last without a power supply.

(V*mAh)1000 = Wh

Wh W=t


Let’s say that laptop has 90 W (calculated from the previous section).

On the battery, we find that it has 19 V and 4800 mAh.

(19 V*4800 mAh)1000 = 91,2 Wh

91200 Wh 90 W=1 h

Note: The number you get is considered if you run your laptop on max capacity (max screen brightness, running a lot of applications simultaneously, performing a lot of graphic tasks, playing games, etc.). So the real number on average load will be 5-7 times higher.

Find tips on how to consume less energy below.

LaptopTips: how to consume less power

The following tips will help the battery lasts much longer:

  1. Pick the right laptop. Buy a gaming laptop if you really aimed at playing games most of the time. As most of the gaming laptops have shorter battery life than other laptops
  2. Screen brightness. We recommend reducing screen brightness, in this way the laptop will use less battery energy.
  3. Unplug unnecessary devices. If you don’t use a web camera or external speakers, it is better to unplug them as the cables also take some power from your laptop even if you don’t use external devices.


Calculation of how many watts your laptop uses is very easy and usually indicated on the laptop label. By knowing this number you will be able to figure out how many hours your device will last without a power supply. It is extremely helpful if you need to use a laptop in places without a constant power supply.


🕒 How many watts does a laptop use per hour?

It depends on the laptop’s specs, e.g. laptops with a bigger screen, more powerful processor, and video card will consume more. But in general, the laptops use 50-100 Watts per hour.

💻 How many watts does a 17-inch laptop use?

A number will depend on the model you have, usually, their adapters have 90 Watts. In our article, you can get to know the exact number of watts just in 2 easy steps.

🔌 Is it ok to leave a laptop plugged in all the time?

Keeping a laptop plugged in all the time won’t damage your battery if you pay attention to whether the battery heats up (you should avoid it). You can always increase your battery life, find out how in our article.

⏳ How many hours we can use a laptop continuously?

It depends. The tech specs, load on the laptop, how powerful the battery is directly effected how long it will last. But there is an easy formula that helps to calculate the time.

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