Cost of electricity

Electricity companies bill customers for the electrical energy they use.

A joule is much too small a unit of energy and so the electricity companies use units called kilowatt-hours, kWh.

Domestic electricity meters measure the number of units of electricity used in a home or other building.

The more units used, the greater the cost.

The cost of the electricity used is calculated using this equation:

total cost = number of units used × cost per unit

The cost per unit is set by the electricity company, for example 14.78 p per kWh.

This means that each unit of electricity costs 14.87 p.

An electricity bill has two important numbers: present meter reading and previous meter reading.

The number of units used is the difference between these two readings.

Electricity bill: present reading = 40745 kWh; previous reading = 39990 kWh

Present reading = 40745 kWh

Previous reading = 39990 kWh

Number of units used = present meter reading - previous meter reading

= 40745 – 39990

= 755 kWh

total cost = number of units used × cost per unit

= 755 x 14.78 p

= 11159 p

The cost of electricity used is £111.59

Question

Use the following information to calculate the cost of electricity used.

Previous reading = 37070 kWh

Present reading = 38217 kWh

Units at 14.78p per kWh.

Number of units used = present meter reading - previous meter reading

= 38217 – 37070

= 1147 kWh

total cost = number of units used × cost per unit

= 1147 x 14.78p

= 16953 p

= £169.53

The cost of electricity used is £169 .53.