Sufficient Copper Thickness for 5V 4A
There are a number of standards that provide some requirements/recommendations for determining trace width for given currents. There are several factors that come into play, such as the copper weight (thickness), expected ambient temperature, and allowed trace temperature rise. See the table below:



A graphical representation is also shown below:



IPC-2221 covers trace width requirements, and a number of websites out there have calculators based on IPC-2221. A few examples are:

Qorvo

4PCB

7pcb

SMPS

EEWEB

At their hearts the functionality is pretty much identical, so take your pick.

You might also consider a tool such as the Saturn PCB Design Toolkit which I have found to be extremely useful in designing my own projects. Off the top of my head I can't remember if it has trace width requirements based on given inputs but it might be worth checking out. In most cases, however, the above table will serve you well enough.