When electric charge moves through a region, it produces an electric current. Current measures the rate at which charge crosses a chosen surface:

$$I=\frac{\Delta Q}{\Delta t}$$

for an average over a time interval.

The SI unit is the ampere:

$$1,\mathrm A=1,\mathrm{C/s}.$$

Conventional current

By convention, current direction is the direction positive charge would move. In a metal, electrons usually drift in the opposite direction because they carry negative charge.

Current is not charge

A wire can carry a steady current without accumulating charge continuously at one end. In a steady state, charge entering a section is balanced by charge leaving it.

Microscopic picture

A conductor contains mobile charge carriers. An applied electric field creates a small net drift superimposed on their microscopic motion. The collective flow produces the macroscopic current.

Current provides the moving-charge quantity needed to describe resistance, circuits and magnetic fields generated by electrical currents.