**COMMERCIAL UNIT OF ENERGY**

The unit joule is too small and hence is inconvenient to express large quantities of energy. We use a bigger unit of energy called kilowatt hour (kW h).

kWh = (Watt x hour ) / 1000

**What is 1 kW h?**

Let us say we have a machine that uses 1000 J of energy every second. If this machine is used continuously

for one hour, it will consume 1 kW h of energy. Thus, 1 kW h is the energy used in one hour

at the rate of 1000 J s^{–1 }(or 1 kW).

1 kW h = 1 kW ×1 h

= 1000 W × 3600 s

= 3600000 J**1 kW h = 3.6 × 10 ^{6 }J.**

The energy used in households, industries and commercial establishments are usually expressed in kilowatt hour. For example, electrical energy used during a month is expressed in terms of

**‘units’.**

*Here, 1 ‘unit’ means 1 kilowatt hour.*