Count and measure

Home energy audit

List the appliances at home, work out the daily units used and find ways to save.

Free1 hour, plus 1 weekEasy

Jump to the steps
Watts × hours ÷ 1000Fan70 W8 h0.56TV80 W3 h0.24Bulbs36 W5 h0.18Total per day0.98Count every appliance

The big idea

You cannot save energy until you know where it goes. An audit counts what each appliance uses, so you can see what matters.

You will need

Tick things off as you gather them.

Step by step

  1. List every appliance

    Walk round your home and list everything that runs on electricity: bulbs, fans, TV, fridge, phone chargers, pump, iron, and so on. Note how many of each.

  2. Find the power in watts

    Look for the sticker on the back or bottom of each appliance. It shows the power in watts (W). If you cannot find it, use a typical value: LED bulb 9 W, ceiling fan 70 W, television 80 W.

  3. Estimate the hours

    Ask the family how many hours each appliance runs on a normal day. Be honest.

  4. Work out the units

    For each appliance: watts × hours ÷ 1000 = units per day (kilowatt hours). For example, a 70 W fan for 8 hours uses 70 × 8 ÷ 1000 = 0.56 units.

  5. Add it up

    Add the units for all appliances to get a daily total. Multiply by 30 for a monthly figure.

  6. Check against the bill

    Compare your monthly total with the units on the electricity bill. Are they close? If not, what did you miss?

  7. Plan some savings

    Pick the three biggest users. Suggest how to cut them: switch to LED, turn off at the wall, use a fan at a lower speed, and so on. How many units a month would you save?

What to look for

  • A few appliances usually account for most of the units.
  • Small standby loads add up when many run all day.
  • Switching old bulbs to LED saves a surprising amount.
Example daily units by appliance (units per day)
Ceiling fan, 70 W for 8 h
Television, 80 W for 3 h
4 LED bulbs, 9 W for 5 h
Phone charger, 5 W for 3 h

An example of the pattern you should see, not measured data. Your numbers will differ, and that is fine.

Why it works

Energy used depends on two things: how powerful the appliance is, and how long it runs. A powerful appliance used briefly can use less than a small one left on all day. The unit on your bill is the kilowatt hour, which is 1000 watts running for one hour. Counting it yourself shows you where your family's power really goes.

Try this next

  • Repeat the audit after making your changes and see how much you saved.
  • Work out how much solar your home would need to cover your units.
  • Share your top tip with the class.

Link to the grid

The grid has to make exactly as much power as everyone uses, every second. Saving units at home lowers demand, especially in the evening peak.

Learn how the grid works

More count and measure experiments

Count and measure

Energy-use survey of the school

Count the bulbs, fans and hours used, then work out how much solar the school would need.

FreeA week, in class groups