As the name suggests, current density is literally the measure of an electric current's density.

You'll see it denoted as the vector symbol 'J'.

In technical terms (in the field of **electromagnetism**) it's the measurement of an electric current (in amperes) per cross-sectional unit area (in meters squared / m^{2}).

### How It Works

Imagine a cylindrical metal rod laid out in front of you. The rod has an electric current traveling through it (which, as you may already know, can only travel in one direction).

Now imagine somehow slicing that rod in half.

The circular area you've created is what's known as the cross-section. Calculating the current density tells you the amount of current that's flowing across a given part of it.

And, importantly, this is a vector quantity. Meaning it has both a magnitude and a direction.