Computers & Laptops

Laptop Power Consumption Calculator

How much energy a laptop uses over a working day, and what it costs if you add your rate.

5 inputs Free, no sign-up

Your figures

From a plug-in meter at the wall, or from the battery figure: a 56 Wh battery that lasts seven hours is drawing about 8 W. The charger's rating is a ceiling, not a reading - a 65 W charger does not mean a 65 W laptop.

Optional. Add it to see what the energy costs.

Try an example

Result

Your result

Enter your figures and the result appears here.

Estimates only. Rates, fees and specifications change. Confirm against the official source before you rely on a figure — see our disclaimer.

About this calculator

A laptop draws far less than its charger is rated at. A 65 W charger on a machine browsing the web is often supplying eight or ten watts; the rating is what it can deliver while charging a flat battery under load, not what the machine uses.

Enter what yours actually draws and this gives the energy over whatever period you are interested in.

How to use this calculator

  1. Measure the draw with a plug-in energy meter, or work it back from the battery: energy in watt-hours divided by the hours it lasts gives the average watts.
  2. Enter how long the machine runs.
  3. Add your electricity rate if you want the cost as well.

The formula

Energy = Power x Time / 1000     (kilowatt-hours)

Working the power back from the battery: a 56 Wh battery lasting seven hours is 56 ÷ 7 = 8 W average.

SymbolMeaningUnit
Power What the laptop draws W
Duration How long it runs h

Worked example

A laptop drawing 30 W for eight hours:

Energy = 30 x 8 / 1000 = 0.24 kWh

Under a quarter of a unit for a full working day — about ₹2 at ₹8 a unit.

Notes and limits

  • A laptop's draw swings widely: idle with the screen dim against a compile or a game can be five times apart, and the screen itself is a significant share on a bright display.
  • The charger keeps drawing a little even when the battery is full and the machine is off.
  • Measuring at the wall includes the charger's own conversion losses, which is what you pay for. A figure read from software does not.
  • For a monthly bill rather than a session, the laptop electricity cost calculator works in hours a day.

What this calculation assumes

  • The power figure is one you entered and is treated as constant, which is an average at best.
  • Nothing about any laptop is assumed anywhere on this page.

Frequently asked questions

How many watts does a laptop use?

It depends entirely on the machine and what it is doing - commonly somewhere between 10 W and 60 W, and much more for a workstation under load. This page will not assume a figure, because the range is too wide for one to be useful.

Is the charger rating the same as the power draw?

No. A 65 W charger is rated for the worst case - a heavy load with a flat battery charging at the same time. Ordinary use is often a fifth of that.

How do I work out my laptop's draw without a meter?

Divide the battery's watt-hour figure by how many hours it lasts on a charge. A 56 Wh battery giving seven hours means an average of about 8 W, which is the machine without the charger's losses.

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