Electrical Energy Use in the
Home
In an electric meter in your home,
the electrical energy is measured in
kilowatt hours (kW x h).
• There are 3 600 000J in one kW x h, therefore
it is much more practical to use kilowatt hours.
1 kW x h = 1000W x 3600s = 3 600 000 W x S = 3 6 00 000J
• A kilowatt hour refers
to 1000 watts being
used over an hour,
therefore a 100W
bulb would have to be
on for 10 hours to
equal 1 kilowatt hour.
• The electrical
meter in your home
records the total
amount of
electricity used in
your home.
• In order to calculate the cost of electrical
energy used in your home you can use the
following formula:
Cost = Power (kW)
x
time (h)
x
rate ($)
Appliances
Average
Monthly
Approximate
power
W Energy Use Costs $
kW x h
Air
conditioner
750
90 - 540
7.20 – 43.30
Clothes
Dryer
5000
50 - 150
4.01 – 12.03
Television
80
5 - 15
0.41 – 1.20
Lighting –
60W bulb
60
5 - 30
0.40 – 2.41
Microwave
Oven
1000
5 - 20
1.40 – 1.60
Example A
• Calculate the cost of the electricity needed to
operate a refrigerator/freezer (500W) for a
day if the rate charged for electricity is $0.08/
kW x h
First convert watts to kW
500W
x
1kW/1000w = 0.500kW
Cost = p x t x rate
Cost = 0.500kW x 24hrs x $0.08/ kW x $0.96
1. Calculate the cost of running a coffee
maker that has a power rating of
0.900kW and operates for 17 hours. (rate
is $0.08/ kW x h)
Cost = 0.900kw x 17h x $0.08/ kW x h = $1.22
2. Calculate the cost of a 1.5kW electric
kettle that operates for 0.80h per day for
two weeks.
Cost = 1.5kw x (0.8h x 14) x $0.08/ kW x = $1.34
3. Calculate the cost of a television that has
a power rating of 0.120kW uses in one
week if it operates for 9 hours every day.
Cost = 0.120 x (9h x 7) x $0.08/ kW x h = $7.64
4. Calculate the cost of a computer monitor
and printer if the monthly energy use is 25
kW x h at a rate of $0.08/ kW x h.
Cost = 25 kW
x
h
x
$0.08/ kW
x
h = $2.00