How much does it cost to use a 100 watt bulb for 1 hour

A 100 watt bulb uses 0.1 KWH of electricity per hour

Depending on how much your energy supplier charges per KWH for electricity. The amount you pay will vary from one supplier to another.

There is a full explanation below. But, you can just use this calculator to work it out for you.

You can even send the results to yourself if you wish.


For example:

If you are paying standard energy prices, you may be paying about 16 pence per KWH. Or if you are on one of the cheaper online tariffs, such as First Utility, you may be paying about 11.40 pence per KWH.

cheaper energy meterIt would take 10 hours for a 100 watt bulb to use a kilowatt of electricity

Therefore, I am now stating the obvious – On a standard tariff you would pay about 16 pence for 10 hours use of a 100 watt bulb, or 1.6 pence per hour.

Or with the cheaper online rates you would pay around 11.40 pence for 10 hours, or 1.040 pence per hour

Many People believe a bulb doesn’t consume much electricity. But if you were to count the amount of lights which are left on unnecessarily, with an understanding of how much energy a bulb is using, you will soon see how much money you could be wasting by leaving these lights on.

The prices I have been using for this example are actually almost accurate, although, I have rounded the figures just to make the calculations a bit simpler.


Most energy suppliers, including:

  • Scottish Power
  • npower
  • E.ON
  • EDF Energy
  • British Gas
  • Scottish Hydro Electric
  • Southern Electric

All charge either a 2 tier tariff (No standing charge)

Or a tariff which includes a Standing charge

In a typical household, it doesn’t make much difference which one you opt for. But if you have a home which is rarely occupied, then the No standing charge option would suit you best, as you will not get a bill for a standing charge whilst you have not been in the property.

I have not included additional charges in the KWH prices above for calculating the cost of running a 100 watt bulb.

You would have some additional costs such as a standing charge, or a first tier tariff.

No standing charge example:

Tier 1 – This is where you pay a higher unit rate for the first so many KWH, normally about 900 KWH. You could be paying about 25 pence per KWH on this tier. A typical household would consume about 3300 KWH of electricity per year. This means your annual electricity usage would be charged as so:

Tier 1 – 900 KWH @ 25 pence = £225

Tier 2 – 2400 KWH @ 12.5 pence = £300

Your total bill for the year would be £525

Standing charge example:

If your standing charge is 30.8 pence per day, your annual standing charge is £112.42

Standing charge = £112.42

3300 KWH @ 12.5 pence = £412.50

Your total bill for the year would be £524.92


The above figures are for example purposes only. This is so you can see the difference between the standing charge and the no standing charge option for a typical household consuming 3300 KWH of electricity per year.

It is a fairly typical example, and has been constructed to explain the difference between the options. As you can see, there really is no difference. The first tier in a no standing charge option is designed to cover the cost of a standing charge!


14th December 2017: Current average electricity usage is 3100 KWH


  • terrry (#)
    December 12th, 2012

    lights off after reading this.

  • John Gibb (#)
    December 18th, 2016

    A school next to me has 7 outside lights on day and night ok at night but for them to be on all day is a bit much so what do you think the saving cost would be for 6 months

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