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How a meter works

What an electricity meter is measuring, and how a spinning disc turned into a digital display.

2 min read Last updated 3 Nov 2026
A square electricity meter with a small round window showing a spinning disc and a row of number dials.

The short version

An electricity meter counts energy in kilowatt-hours, which are the units on your bill. Older meters did this with a metal disc spun by magnetism, and newer ones use electronics to multiply the voltage and current and add up the result. It builds on power and watts.

I always assumed the meter counted how much electricity flowed in.

It counts energy, not electricity.

The two are not the same thing.

The spinning disc

Inside a traditional meter is a thin aluminium disc. Coils carrying the current from your home make a changing magnetic field, and this makes the disc turn. The more power you use, the faster it spins. A set of gears counts the turns and shows them on the dials as kilowatt-hours.

That is why, in an older meter, you can watch the disc crawl round when only a light is on and race when the kettle boils.

Digital meters

A digital meter has no moving parts. It samples voltage and current to calculate the electrical power being used, then accumulates the energy over time. The total is shown on a display. For a meter that also sends its reading over a radio link, see smart meters.

Reading it

A standard import meter shows a cumulative total that rises as electricity is used. To find the amount used over a period, take one reading, take another later, and subtract. The difference is the number of units used, and your bill multiplies it by the price per unit and adds a daily standing charge.

1 unit = 1 kWh

The reading on the meter is in kilowatt-hours. Your bill is the difference between two readings, multiplied by the price per unit.

Sources: Ofgem: energy terms and kilowatt-hours; standard electrical measurement references. Import and export meters may show separate registers.

Key takeaways

  • A meter counts energy in kilowatt-hours.
  • Older meters use a disc spun by magnetism.
  • Digital meters multiply voltage and current.
  • Your bill is the change in reading times the unit price.

Now you know.

A meter counts energy, not flow.

The disc spins faster as you use more power.

And your bill is the difference between two readings.

Last reviewed 3 Nov 2026

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