Energy calculations

Energy calculations

Set up time


What you need

Energy calculations worksheet


To educate students about the various units of energy, and to show them how to convert between units. They will then calculate the annual energy usage of a light bulb.

Learning outcomes


Your students will learn about the different units of energy.


Using online guides, your students will practice converting between these units.


Your students will apply mathematical skills to calculate how much energy a light globe consumes in a year.


Watts, kilowatts, kilowatts hours, joules … Discuss the units of energy and how they are used to measure electricity consumption.

Discuss strategies for converting between different units before students go online to find tools.

Ask students to predict how much energy a light globe uses in a year. Give them some parameters (e.g. a fridge uses 1-2 kWh in a day).

Discuss the results of the light globe calculations and discuss other appliances the students could measure.

Before you do the audit, have a guess at the number of appliances in your household?
Could you do this sort of activity for your school? Or an entire city?

Time required
30 mins

Extension: Energy ratings explained

Get the low-down on energy star ratings with this simple video that explains all the elements of the ubiquitous sticker. Once students have watched this video, there are many activities, energy calculations and discussions you could explore.

It’s not just appliances that get energy ratings. Energy-efficient homes get great star ratings, too.


Energy consumption numbers on these stickers tell you how much energy an appliance uses in a year.


Reverse cycle air conditioners get their own stickers, because the cooling element uses a different amount of energy than the heating element.


Products that have more stars will generally cost more. Why do you think is so?


For every star added to the sticker, that’s an energy saving of 10 to 30%. Explore energy calculations based on this fact.