Learn the basics of Electrical Engineering.

Basics of Electricity Bills and kWH cost of Appliances

Electricity plays a vital role in our life, it charges our gadgets, powers our equipment and is responsible for running our industries. But this electricity is obviously not a free resource, the power supply companies charge you for using the electricity. In this post you'll learn:

  1. What is the unit of electricity bill
  2. What is wattage rating of equipment
  3. How to calculate your bill
  4. Bill for Charging a mobile phone for 2 hours
  5. The cost of running 1 Ton AC for 6 hours
  6. What is tariff and how "actually companies charge you"

What is the unit of electricity

The basic unit of electricity is kWh and it is the amount of energy which is used by a 1 kW (1000 watt) device for 1 hour. In terms of layman 1 kWh is known as 1 unit. Power companies usually specify the cost of electricity per unit. For example, a company might charge you $0.1 for 1 unit. This means if you are using 200 units (200 kWh) per month your power supplier will charge you $20.

What is wattage rating

Electrical equipment is rated in terms of watts. The higher the wattage rating the more it'll cost you. The approximate wattage ratings of various devices are listed in the table below.

How to calculate your bill

You can easily estimate your electricity bill on the basis of equipment your use. Let's consider you are interested to find the monthly bill of your home for the following appliances:
  1. 2 fans for 10 hours daily [Fan rating: 70 watts]
  2. 3 lamps for 12 hours daily [Lamp rating: 20 watts]
  3. LCD TV for 1 hour daily [LCD: 100 watts]
The charges per kWh are $0.1.
Let's calculate the bill.
2 Fans for 10 hours = 2 * 10 * 70 Wh = 1400 Wh
For 30 days we need to multiply 1400 * 30 Wh = 42000 Wh = 42 kWh

3 lamps for 12 hours = 3 * 12 * 20 Wh = 720 Wh
For 30 days multiply 720 with 30 = 720 Wh * 30 = 21600 Wh = 21.6 kWh

1 LCD for 1 hour = 1 * 1 * 100 watts = 100 Wh
For 30 days: 30 * 100 Wh = 3000 Wh = 3 kWh

Finally summing up the parameters: 42 kWh + 21.6 kWh + 3 kWh = 66.6 kWh
Charges per unit are $0.1 so overall cost for month = $0.1 * 66.6 = $6.66

Let's solve two more examples to better understand it

Bill of mobile phone which is charged for 2 hours daily

A mobile phone is rated at 6 watts.
For 2 hours daily usage, the monthly bill will: 2 * 6 * 30 = 360 Wh = 0.36 kWh
Assuming charges per kWh to be $0.1 multiply $0.1 by 0.36 kWh = $0.036

Bill of 1 Ton AC running for 6 hours daily

1 ton AC is consumes around 1200 watts.
For 6 hours the monthly bill be: 6 * 30 * 1200 Wh = 216,000 Wh = 216 kWh
Assuming charges to be $0.1 kWh the overall cost is 216 * 0.1 = $21.6

What is tariff and How companies charge you

Tariff is the method by which the companies allocate an optimal rate of electricity. The most common type of tariff is block rate tariff. In this type, the electricity units are divided into different blocks. Each subsequent block is charged at different rates. For examples:
1 - 100 units - Block A
100 - 200 units - Block B
200 - 500 units Block C
The developed countries which vast energy resources charged subsequent blocks at a lower price. For example, the 1-100 units are charged at $0.1 per kWH whereas the 100 - 200 units will be charged for $0.05. In developing countries with lower resources reverse happens.


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