Ampere (A)

The ampere is the SI base unit for electric current. It is currently defined by the force created between two infinitely long wires in a vacuum that are carrying the same current.

Amperes, or 'amps' for short, measure electric current, which is a flow of electrons along a wire or ions in an electrolyte, as in batteries. Electric current allows us to power electrical devices, like smartphones or laptops.

The ampere has only been in use for as long as we have had access to electricity – a small proportion of the history of measurement.

It has previously been defined as the current that would cause the deposition of a certain mass of silver per second from a silver nitrate.


In 2019, the definition of the ampere is expected to be replaced by a definition that is more intuitive and easier to realise. Electric current will instead be a measure of the number of electrons passing a certain point on a wire, per second.