Electricity Saving Tips For Homes And Offices

What are Watt, Kilowatt and a unit of electricity

By on October 15, 2014
This article is also available in these languages: hi Hindi

When we get our electricity bills, it shows that we have used a certain number of units for the given period. When we go to buy appliances, most of them have watts mentioned on them. If you find it difficult to understand the relation between the two, then you are not alone. Electricity bill and its components are confusing to many and with this article we will try to explain what are watt, kilowatt and a unit of electricity.

Confused

Power and Energy/Electricity

Power and Energy/Electricity are two words that are used so much for each other that many feel that they mean the same. Interestingly both of them have a very different meaning. Power is the rate at which electricity is used and energy/electricity is the actual consumption. To give an analogy, power is similar to speed but electricity/energy is the actual distance travelled.

So        Power x Time = Electricity (or energy)

Just like          Speed x Time = Distance Travelled.

Power and its units

Power is always represented in watt (W) or kilowatt (kW). A thousand (1000) watts make one kilowatt. So if any appliance is rated as 1.2 kW then it means that it consumes electricity at a rate of 1200 W. Now as we discussed earlier that power is the rate at which electricity is consumed and not the actual electricity consumed, Watt or Kilowatt just represent the rate at which electricity is consumed per hour. Which means that when you buy a 100 W bulb, it does not consume 100 units of electricity but consumes at a rate of 100 W.

Energy/Electricity and its units

A unit (as mentioned on the electricity bills) is represented in kWH or Kilowatt Hour. This is the actual electricity or energy used. If you use 1000 Watts or 1 Kilowatt of power for 1 hour then you consume 1 unit or 1 Kilowatt-Hour (kWH) of electricity. So the reading on the electricity meter represents the actual electricity used. Just like the odometer on your vehicle that shows the actual distance travelled by the vehicle, electricity meter shows the amount of electricity that is used. So a 100-Watt bulb if kept on for 10 hours will consume:

100 x 10 = 1000 Watt-Hour = 1 Kilowatt-Hour (kWH) = 1 units (on your meter).

Estimating units consumed by any appliance

Now with most of the concepts explained we would like to make it easy for you to calculate how much units does any appliance consume. Most appliances have wattage written on them (either on their container box or somewhere on the appliance). Once you have the wattage, next you need to figure out how many hours a day do you use it. After that you can use the formula below:

Daily Units = (Wattage x Usage hours per day) ÷ 1000

Monthly Units = Units x 30 (or 28,29,31 based on month)

Please note that this formula may not work always. For appliances like Air Conditioner, Water Heater, Cloth Iron (any heating or cooling device) and pumps, this will not work.Infographic3

Source of Information:

http://www.energysavers.gov/your_home/appliances/index.cfm/mytopic=10040

http://en.wikipedia.org/wiki/Watt#Confusion_of_watts.2C_watt-hours.2C_and_watts_per_hour


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There Are 37 Comments

  1. Ravi says:

    Hi how to find the electricity meter number and unit consumption in a digital meter.?

    • Abhishek Jain says:

      Hi,

      Meter Number will differ from make to make. For unit consumption you will need previous months reading and current reading.

  2. csk says:

    Good Article :)

  3. pradeep says:

    Sir begging you to give the clarification on TO PRODUCE 1MW OF CURRENT HOW MUCH COAL IS REQUIRED. Because i would like to give paper presentation on current conservation

  4. pradeep says:

    Sir to produce 1megawatt of current howmany tons of coal is required?

  5. aamir says:

    aamir Islamabad
    it is very informative, thnx

  6. Malu says:

    Hi
    I am a student staying at a PG in Delhi and have separate electronic metre installed for my room. A ceiling fan and tubelight are the only electronic gadgets i use in my room. In my previous PG i used to keep both the tube light and ceiling fan switched on for longer time since the room was dark and dingy.The ceiling fan was used almost for the whole day excepting 3-4hrs depending on my class timings. Whereas the tubelight would be in use for nearly 12hours a day. Then electricity consumption came around 44 units per month.
    However, now i shifted to a new PG. Here i do not use tubelight for more than 6-7hrs a day as the room has good ventillation and is not dark.The usage of ceiling fan is same as that of my previous PG. However, I found that if I a spent an entire day in my room with the ceiling fan running and tubelight switched on for 6-7hrs, the electiricty consumption is 3-4 units per day. I believe this is abnormal as by the end of the month i’ll have to end up paying for nearly 90units of electicity(for a ceiling fan and tubelight), that too after my electricity consumption having gone down from that of my old PG. I have asked the land lady to get the metre checked, but she is saying that its normal and she will bring her electrician to check the metre. Kindly advice on what is to be done.
    Malu

    • Abhishek Jain says:

      Hi Malu,

      A regular ceiling fan consumes about 75-90 watts depending on the efficiency of the fan. Assuming that it is most inefficient 90 watt fan. Then in 20 hours it would consume (90*20)/1000 = 1.8 units a day or 54 units in a month. If we assume that it is 75 watts fan then it would consume 1.5 units a day or 45 units a month.

      So from the fan itself the power consumption is more than 44 units. I think your old place had electromagnetic meters which tend to slow down with time (and that is the reason why DISCOMs shifted to electronic meters).

      Now coming to tubelight. Again I assume that you have regular T8 tublight which is about 45-50 watts (it may be a bit more than that as well). Assuming 50 watts in 12 hours it would consume (50*12)/1000 = 0.6 units, so in a month that will be 18 units. In 7 hours it would consume (50*7)/1000 = 0.35 units, so 10.5 units a month.

      So ideally your old bill should have been about 50 + 18 = 68 units. And your new bill should be about 50 + 10.5 = 60.5 units.

      Now you have only considered fan and tubelight. Please make sure that you are not using any laptops, refrigerators, any other appliance that works on electricity. If you do not have any other appliance then 90 units is on higher side.

      Also if you use your fan for 24 hours then it would consume about (90*24)/1000 = 2.16 units a day or about 65 units a month. If the fan is really old and not maintained well then it might also go up to usage of 100 watts.

      You can certainly get your meter checked, but ask the electrician to check wattage of each appliance.

  7. krishan says:

    unit 111 convert into killowatt

  8. online king says:

    thank you vermuch also please update home appliances and their capacity

  9. SATISH KUMAR VIJ says:

    Dear Abhi,

    The make is Haier(2013) & Voltas(2014).

    Place is Ambala

    thanks.

    • Abhishek Jain says:

      Hello Mr Vij,

      A BEE 2 star rated 1 ton AC would be rated to consume 1150-1200 watts power. The AC is rightly sized only if the room does not get direct sunlight on the roof/walls. Else you need about 1.3 tons of cooling. Assuming it is rightly sized, then an AC rated at 1150 watts would be on for about 70% time in peak summer (when outdoor temperature is about 48 and you keep thermostat temp at 28), then power consumption in an hour would be (1150/1000)x0.7 = 0.8 units. If the AC is undersized it might increase to 0.9 or 1 unit per hour. If it is highly undersized (which should not be the case if your room is 11×10), then the total can go up to 1.15 units per hour (assuming it is 100% on). Also it may consume more than that as well in case the outdoor unit is directly facing the sun. Because 1150 watts is power consumption in ideal situation. If the outdoor unit faces sun, then condenser efficiency goes down and it starts taking more current. 7 units in 6 hours means that the compressor is not stopping or the temperature setting on thermostat is not getting attained in the room. I hope you keep the rooms tightly closed (doors as well as windows) when you switch on the AC.

  10. SATISH KUMAR VIJ says:

    I HAVE 2 ACS OF ONE TON 2 STAR EACH. I HAVE SET THE TEMP AT 28 DEGREES WITH FAN ON. THE ACS ARE RUN FOR 6 HRS DAILY IN THE NIGHT. THE ROOM SIZE IS 11X10. I HAVE NOTICED THAT THE UNIT CONSUMPTION IS VERY HIGH AFTER NEW METER HAS BEEN INSTALLED. I HAVE CALCULATED THE UNITS OF AC CONSUMPTION TO BE 14. IS IT RIGHT? BECAUSE WITHOUT AC MY CONSUMPTION WAS 8 UNITS & NOW IT IS 24 UNITS ON AVERAGE

    • Abhishek Jain says:

      Hello Mr Vij,

      What is the brand/model that you have purchased? 7 units in 6 hours certainly looks on a higher side at temperature of 28 degrees. Are these new ACs or old ACs?

  11. Raj says:

    Hi Abhishek ,

    I want to how much electricity is required to pump xxx (eg: 100 gallons) of water to the 2nd floor water tank from ground floor?

    I just want to know units consumed….!!

    Thanks,

    Rj

    • Abhishek Jain says:

      Hi Raj,

      Essentially by moving water two floors we are changing the potential energy of water. The change in potential energy is

      mass x gravity x height

      100 gallons is almost 378.54 kg
      gravity is 9.8 m/s2
      height let’s assume is 25 ft or 7.63 mts

      so energy is 378.54 x 9.8 x 7.63 = 28267.85 joules = 0.008 kWH.

      Now assuming efficiency of pump is just 45% then pump would consume 0.018 units of electricity.

  12. Ganesh says:

    Please clear my confusion

    What is Ah w.r.t domestic electricity ?
    When somebody tells that we have electricity with Ah what does it mean?
    do Ah allows run more equipment with more watt usage?
    what is the maximum watt can be consumed by any equipment without Ah(without any additional transformer or stabilizer for ex immersion coil also I know that watt consumption is depend on item which we purchase but I am speaking about maximum watt item which we can run without ah, I need that maximum watt) for domestic electricity in india?
    How volts affects the watts?
    also finally whats the maximum watt can be consumed by any equipment with Ah

    Kindly don’t give explanation with formulas I am weak in mathematics :)

    • Abhishek Jain says:

      Ah is typically used for batteries and represents the amount of energy it can store. Every battery has certain voltage and VAh is a unit for energy (A 12 V battery of 150 Ah size can store 12×150 VAh energy). Watts is rate at which the energy is used. Now not all of the VAh can be used and thus useful energy (Wh) is roughly 0.8 of the total VAh value. So Wh (or watt hour) the above battery stores = 12x150x0.8 = 1440 (approx). And so if you have a 10 watt bulb you can run it for 1440/10 = 144 hours.

      Sorry I could not explain it to you without formulas.

  13. surinder bansal says:

    i have i ton o genral ac how many unit per hours.

  14. Shalini says:

    Hi i have one 1.5 ton 5 star ac 1480 watt.
    I run it at 25-30 c° 90% of the time and 10% of the time it runs at 16c° for an average of 10 hours a day(6 days in a week in day time) and 1day 15 hours throughout the day.
    What’s going to be the monthly unit and the electricity bill.? We pay rs8 per unit.
    Also tell me how to read the meter.
    Suppose it shows 21 so is it 21 unit or 2.1 unit?

    Need your help asap. Thank you in Advance bro.

    • Abhishek Jain says:

      Hi Shalini,

      If the AC is rightly sized (not undersized or oversized), it should consume about 1 to 1.1 unit in an hour when you run it at 25 to 30. At 16 it will go up to 1.3 or 1.4 units an hour (both assuming temperature outside is not more than 35-36).

      Meter always shows the absolute number and there are no decimal places in units. And when calculation happens it is previous reading minus current reading in units.

  15. Rusi says:

    How to calculate the total electricity load of a typical flat .
    How to figure out whether the meter required would be 3 phase or Single phase.

    • Abhishek Jain says:

      Hi,

      If you can provide a list of appliances that you have, we can help you calculate the load. To choose between single and 3 phase, you can read this: https://www.bijlibachao.com/electricity-bill/what-are-single-phase-and-three-phase-connections-and-how-to-choose-between-the-two.html

  16. surya says:

    good article. SIr, a 1.5 ton AC would require approximately 5KW power,isnt it? If Iam correct then how many units does it consume for 1-hour.If im wrong,please help me in converting ton to KW

    • Abhishek Jain says:

      Hi Surya,

      Typically 1.5 ton ACs require 1.4-2 kW of power depending on BEE star rating. 5KW is a lot. Although there are several factors on which electricity consumption depends as listed on this page: https://www.bijlibachao.com/air-conditioners/things-that-impact-electricity-consumption-in-air-conditioners.html …. but to do a very high level calculation we assume that AC compressor is on for 70% time. So in 1 hour a 2 kW AC would consume 2 * 0.7 = 1.4 units of electricity (typically at temperature of 22 on thermostat and outside temperature of 34).

      Also ton is not directly proportional to power consumption. It is proportional to cooling capacity kW.

      • pratibha says:

        how much kilowatt meter should be connect to1 ton a.c or for 1.5 ton a.c 3 star for home.(single a.c)

      • Gurpreet says:

        hello there ,i brought onida AC in 2007 jispe likha hai 4500Kcal/h ..
        bhaut bijli khaata hai ,, kyaa kru ???
        Ac bhi lagwaaya aur chlaa bhiu nahi sakte :-\

        • Abhishek Jain says:

          sir aap 25-26 par AC chalao, saath mein pankha chalao. Aur yeah bhi dekho ki room band hai aur bahar ki hawa andar nahin aa rahi hai. Try applying some insulation techniques that we have mentioned on this link: https://www.bijlibachao.com/save-electricity/insulation …. garmi ka ghar mein aana kam kar do AC ka bill waise hi kam ho jayega :)

  17. Deepak says:

    You have written…

    “For appliances like Air Conditioner, Water Heater, … , this (formula) will not work.”

    Why ? Is it because, e.g. for Window AC’s if the specs says 1130 Watts, does it means with the compressor running ? So actual units consumed may be less as the AC is cut-off on reaching the desired temprature?

    Even then, your formula should atleast give approximation ? Atleast it can be helpful while comparing between two products?

    • Abhishek Jain says:

      That is right. In ACs, Water Heaters and Electric Iron there is a thermostat that switches off the appliance when the appropriate temperature is reached. In ACs, the compressor goes on and off and the peak watts mentioned on the specs is when the compressor is on. The units consumed in AC depend on several factors as mentioned in this post: https://www.bijlibachao.com/air-conditioners/things-that-impact-electricity-consumption-in-air-conditioners.html

      As an assumption while doing payback calculation we take actual unit consumption to be 0.7 x (AC watts). So 1130 x 0.7. But that is very high level approximation. Temperature setting on thermostat plays a very important role. In some tests that we have done on our own AC, we observed that a 1.5 ton window AC which is rated at 1990 watts consumed:

      1.4 units at 22 degrees without ceiling fan which is about 0.7 times 1990
      1 unit at 26 degrees with ceiling fan on (giving same comfort as AC at 22 degrees)
      0.8 unit at 26 degrees without ceiling fan.

      If you keep it at 18 degrees it will be more than 0.7 times the power. Also it will depend on the size of the room. If you put a 1.5 ton AC in small room, it will cut off quickly and will also consume more electricity. If you put 1.5 ton AC in a huge room, it will run the compressor continuously. So an approximation itself will be highly approximate :).

  18. Vinod says:

    Great help…. Thanksss

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