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Watts, Amps and Volts and How To Understand Electricity

Updated on May 02, 2016
Rik Ravado profile image

Rik is an Engineer who has held a range of marketing, technical support and management roles roles and is also a qualified teacher.

Joined: 9 years agoFollowers: 782Articles: 85
Watt is the Amp and Volt? Simple Electrical Circuit with a Bulb, some Wire and a Battery
Watt is the Amp and Volt? Simple Electrical Circuit with a Bulb, some Wire and a Battery

So What Are Watts, Amps and Volts All About?

A guide to the basics of electricity. Here is everything you need to know about electrical power (Watts), current (Amps) and voltage (Volts), how to understand simple electricity and the way these parameters relate to one another.

Lets begin with some simple definitions:


Electricity consists of the flow of electrons through a conductor such as an electric wire. You can’t see electrons but a helpful analogy is to think of electricity as the flow of water through a pipe.

We measure the rate of flow of electricity as an electric current (just as we think of the rate of flow of water in a river as the river current). The letter used to represent current in an equation is I.

Electric current is measured in Amperes, shortened to Amps or simply the letter A.

A current of 2 Amps can be written as 2A. The bigger the current the more electricity is flowing.


So what makes the current flow in the first place? A device such as a battery provides what is known as a potential difference in an electric circuit.

If we go back to our water analogy, the battery is like a water pump that propels water through a pipe.

It creates pressure in the pipe causing the water to flow. So how do we measure this pressure? We call electrical pressure Voltage and measure it in Volts, shortened to V. The letter V is also used represent Voltage in an equation.

A voltage of 3 volts can be written as 3V.

The bigger the voltage the higher the pressure and the more current flows. But in order for the current to flow, the electrical conductor or wire must loop back to the battery.

If we break the circuit, with a switch for example, then no current will flow.

Electric Current


Before we get onto Power and Watts we need to understand Resistance. The letter R is used to represent resistance in an equation.

In the case of our battery, if we short circuited it with the wire (no bulb), the wire and battery would get very hot and the battery would soon be flat.

That is because there would be virtually no resistance in the circuit so a huge electrical current would flow until the battery was empty.

But once we add our bulb to the circuit, the bulb offers a lot of resistance and creates a local 'blockage' (or narrowing of the pipe) where the current finds it hard to flow.

This greatly reduces the current flowing in the circuit which means the energy in the battery is released more slowly.

As the battery forces the current through the bulb the battery's energy is released in the bulb in the form of light (and heat).

In other words, the current carries stored energy from the battery to the bulb where it is turned into light and heat energy.

Resistance is measured in Ohms or Ω (Omega) for short.

So 5 Ohms can be written 5Ω.

Watt is the Amp and Volt? Electrical Resistance
Watt is the Amp and Volt? Electrical Resistance
Watt are Amps and Volts?
Watt are Amps and Volts?


So how do Current and Voltage relate to one another? Well, the bigger the current the brighter the light and similarly the bigger the voltage the brighter the light.

Both the voltage and the current in the bulb determine how much energy is released in a certain time.

The Watt is a measure of power or how much energy is released per second. It can be shortened to W.

1 Watt can be written 1W.

We can calculate the power released in a bulb by multiplying the voltage in Volts across the bulb by the current in Amps flowing through the bulb (W = V x I).

For example a current of 2 Amps flowing through a bulb with 12 Volts across it generates 24 watts of power.

In the UK, domestic power is supplied at 240 Volts. A 100 Watt bulb will therefore draw a current of 100/240 Amps (about 0.4A). This means a 1A fuse can be safely added to the mains plug of a desk lamp with a 100W bulb because 1A is much greater than 0.4A.

In the USA, the domestic supply is typically 110V, safer than the UK, and this means a 100W bulb draws a current of 100/110 Amps (about 0.9A).

Simple Calculations

These simple calculations are summarised in the formulae in the circle to the right. So, for example, we can calculate the power in Watts (see orange area top left of the circle) as V x I.

Hopefully now you now understand the difference between electric current, measured in Amps, voltage, measured in Volts or electrical power measured in Watts.

Finally, remember that if you know the voltage of your power supply then you can calculate the current through a bulb, fuse or other electrical appliance or component, based on its rating in Watts.

Electricity Quiz - A couple of questions to try

Electricity Video


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    • LiamBean profile image

      LiamBean 7 years ago from Los Angeles, Calilfornia

      Lovely. Wonderful explanation of Watts, Amps, and Current.

    • Rik Ravado profile image

      Rik Ravado 7 years ago from England

      LiamBean - glad you found it helpful!

    • elkangorito 6 years ago from Thailand

      Even though your blog is an excellent "guide to the basics of electricity", there are a couple of things that need to be considered:

      You said, "In the USA, the domestic supply is typically 110V, much safer than the UK."

      This is not true.

      Firstly, the voltage in the UK is officially 230v (single phase, domestic).

      Secondly, the voltage in the USA is 120v (domestic).

      120v is in no way "safer" than 230v. A "safe" voltage is considered to be less than 50v RMS (AC) or 120v DC (ripple free). These voltages are known as "extra low voltages" & relate to "touch voltage limits".

      You also said: "Finally, remember that if you know the voltage of your power supply then you can calculate the current through a bulb, fuse or other electrical appliance or component, based on its rating in Watts."

      I think that you meant to say, "Finally, remember that if you know the voltage of your power supply then you can APPROXIMATELY calculate the current through a bulb, fuse or other electrical appliance or component, based on its rating in Watts."

    • Rik Ravado profile image

      Rik Ravado 6 years ago from England


      Thanks for your comments - I still maintain 120v is safer than 230v. In other words the lower the voltage, the less current potentially flows through the victim.

      I agree with your 'approximately' as obviously cable and other elements in the circuit will further lower the current. Also the rating of the bulb or other appliance will not be precise and there will be a margin of error.

      Thanks for stopping by and commenting!

    • Peter Enmore 6 years ago

      Yeah, you really can't get the calculation it to an exact. But you can definitely get an approximate.

    • Rik Ravado profile image

      Rik Ravado 6 years ago from England

      Thanks Peter!

    • Kevin 6 years ago

      Thanks for this mate.

      Helped a lot with my schoolwork. :P

    • bernie 6 years ago

      Everyones a cridic. I understood completely and I understood that it is not on the money, and those of us who don't have to act like know it all's realize that there are factors involved that makes the math close, but there is room for error. Maybe thicknees of the wire being used, battery losing power, or whatever the reason. People chill!!! If I understood and realise this then you brain childeren should. Anal Bastards.

    • topquark profile image

      topquark 5 years ago from UK

      Useful and well-presented article! A lot of people seem to get confused about Watts and Amps and Volts - an explanation like this has been long overdue.

    • bert k 5 years ago

      thanks for the free lesson. you made it very clear and easy to understand. here is a smart formula i'd like to pass on to beginners like myself. U+P=R or utilization plus practice equals retention. i wish there had been internet and google when i was a kid. best regards teach. bk

    • Rik Ravado profile image

      Rik Ravado 5 years ago from England

      Thanks for the feedback Bert - you are so right with U+P=R.

      Learning is much more effective when you put what you have learned into practice!

    • Brett 5 years ago

      Shouldn't your graphic read I = sqrt(P) / R instead of I = sqrt(P) / V?

    • Rik Ravado profile image

      Rik Ravado 5 years ago from England


      Well spotted - I agree. (Changed the graphic) Thanks!

    • Robert 5 years ago

      First, thank you does not say enough for this. I am a slow learner and forward to using this to help learn about electricity. I am finding out that it is not that hard, but like Bert K commented, U+P=R. Thank you again so much Mr. Ravado

    • Ak 5 years ago

      Clear as crystal

    • Ak 5 years ago

      I have a question.. Can the magnetic energy be converted to electric enegergy somehow by properly placing them on a flywheel? Rotating the flywheel using the magnetic force. There are lot of things going on the web about it. And how come they only sell guides but not the finished product.

    • Rik Ravado profile image

      Rik Ravado 5 years ago from England

      Ak - These products are all scams. You don't get electrical energy for nothing. You can convert mechanical energy into electrical energy, a generator does this. But you still have to put the same amount of energy in. Scammers sometimes talk about perpetual motion in connection with free energy but it doesn't exist.

    • Ak 5 years ago

      Thanks for the heads-up Rik. I want to implement cheap renewable energy, could you outline few options? Pv or solar panels are not the options where i live. I heard a lot about fuel cells, are they expensive?

    • ajay 4 years ago

      how do we determine the maximum limit of ampereage that can be drawn out of a 120 volts line

    • Rik Ravado profile image

      Rik Ravado 4 years ago from England

      ajay - the maximum current would depend on the fuse or breaker in the circuit. In theory, if you short circuited the 120v you could get an infinite current but domestic supplies normally have a breaker that trips if you draw too much current. In the UK, our domestic circuits typically allow you to draw about 13A from a 3 pin plug but it my be higher elsewhere, for example the US.

    • ajay 4 years ago

      thanks for the answer. sir please give one more answer about transformers. I read somewhere that transformers can increase and decrease the voltage of a said line, so in that case is it possible to decrease the incomming 220v main line of my house to say 24v and then again increase it 220v for normal usage. will the performance be the same and will it decrease the electric bill.

    • saratchandra 4 years ago

      Good explanation with examples

    • amped 4 years ago

      Very useful explanation.

    • Kiran Chandran 4 years ago

      I had cleared many doubts by using this........

    • Rusty 3 years ago

      I found it interesting that elkangorito said no way 120 is safer than 230 volts. Then why in England on ALL commercial work sites the max voltage used is 120? Everything is stepped down from 230 to 120.


    • Alex 3 years ago

      Can someone help to find out 12 volt ??? w required in the given satiation?

      I required 220 volt 1000 w to run my application. i am planning to install solar panel to have full fill my requirement. it involve solar panel ,12 volt battery, and power inverter, how many watts of 12 volt panel do i required to have 220 volt 1000w power to run my application

    • vikas pal 3 years ago

      great blog

    • Diz 3 years ago

      Illustrated beautifully with a photo of Naomi Watts (wtf?) - clearly all this electrical stuff is about tits. Nice touch.

    • Alpo 3 years ago

      Thanks for the has been awhile and was looking for the basic equations. According to your article, "A" is short for amperes or amps. Later, "I" is introduced without relating it to amps. For clarity, you might add that.

    • santosh kumar 3 years ago

      Thanks a lot for your wonderful detail explainatin. I hope it would be very helpful to all beginers. Best wishes for your blog.

    • Someone 2 years ago

      That was useful thanks

    • MARJ WATSON 2 years ago

      Please advise this old lady if I can use Gu10 replacement bulbs with 110/220 in the uk, as I bought them in error, thanking you in anticipation,


    • sanjay 2 years ago

      Very good

    • SAQIB6608 profile image

      SAQIB 24 months ago from HYDERABAD PAKISTAN

      Being engineer myself I enjoyed reading the concepts.

    • jeo 4 months ago

      hi there, i am just getting to know about electricity. and has always been confused to hell, what is Amps, Volts etc. now i understood it all.

      thanks for the article. God Bless

    • ade 3 months ago

      amazing, never been able to get this stuff in my Head and you've managed it so succinctly mate, thanks ever so much, Cheers

    • Nancy Marine 3 months ago

      I got 2/2 of the question, I guess I know watt is watt.

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