Our energy glossary explains some of the main terms you're likely to hear.


Big Six

These are the six major energy suppliers in Britain, which are:

  • British Gas
  • EDF
  • E.ON
  • NPower
  • Scottish Power
  • SSE

Calorific value

A measurement of energy that is generated when gas is combusted, which is recorded in cubic feet (ft³) or cubic metres (m³).

Dual fuel

This is when the same supplier provides both gas and electricity on the same tariff. There are usually discounts available if you spring for a dual fuel tariff.

Economy 7

A tariff that offers cheaper unit rates for 7 hours during night time (usually from 0000-0700). Economy 7 meters show two separate readings.

Economy 10

Similar to an Economy 7 tariff, except that it provides cheaper unit rates for 10 hours during the evening.

Kilowatt hour (kWh)

Without getting too technical, a kilowatt hour (kWh) is a unit of measurement for energy usage and it applies to both gas and electricity. It measures the amount of energy used if a 1,000 watt appliance were to run for an hour.

For example, it would take 10 hours for a 100 watt light bulb to use 1kWh of energy. This is why energy saving bulbs like LEDs are more popular; they have a lower wattage and therefore consume fewer kilowatt hours, but they are just as bright as traditional bulbs.

MPAN (Metering Point Administration Number)

Sometimes referred to as an ‘S number’, this number uniquely identifies your household’s electricity supplier, and it is always preceded by the letter ‘S’.

It’s standard format is as follows:

The top row of numbers is (almost) always made up of 8 digits, while the bottom row is made up of 13 digits.

The numbers are separated in the manner shown, as each set denotes specific information as your supplier’s distribution ID.

Alternatively, some energy bills will simply call this your ‘electricity supply number’ as opposed to an MARN.

MPRN (Meter Point Reference Number)

This number identifies your household’s gas supplier, and will comprise anything between 6 and 10 digits.

It is sometimes referred to as an ‘M number’. Your energy supplier may refer to this number as your ‘gas supply number’ rather than an MPRN.


The Office of Gas and Electricity Markets (Ofgem) is a government regulator that promotes competition in the energy industry by regulating the electricity and gas monopoly in Britain.

This means that consumers can benefit from a variety of value-for-money energy tariffs.

Although it works with the UK Government, it is an independent body and it is non-ministerial department.

Standing charge

This is a fixed daily cost added to your energy bill, so it is not dependent on your gas or electricity usage.

This charge covers vital costs such as maintenance, meter readings, and other logistical facets of energy supply and consumption.


This is the amount that your energy provider charges you for your gas and/or electricity usage.

There are many different types of tariffs (e.g. fixed, standard, green) to choose from, depending on your household’s energy needs.

Unit rate OR unit price

The amount you pay per unit of gas or electricity (measured in kilowatt hours).

Wholesale energy

The bulk purchasing of gas, electricity, and other energy products by energy suppliers via the wholesale energy market.

The advanced bulk purchasing of wholesale energy is intended to keep energy prices stable, especially given that wholesale energy costs account for over half of a consumer’s energy bill.

Although the price of wholesale energy is set by the market, it is still prone to fluctuations and this has a direct effect on consumers’ energy bills

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