Trace Width before forking track

Thread Starter


Joined Nov 17, 2017
I'm trying to wrap my head around calculating trace widths and there's loads of information on these forums so I think I am getting a better understanding of how to work this out.

If I am making a PCB that has four motors, and each motor takes 5v 1amp, the total draw from the power source would be 5v 4 amps.

Using the calculator here I can see that if I use 2oz/ft^2 copper thickness I should make the track width around 40mil (approx 1mm).

But since this is a parallel circuit not all the traces will be holding 4 amps.

I have drawn up what I think would be the current traveling through each track.

Screen Shot 2018-04-29 at 22.58.30.png

Does this mean that only the tracks I have labelled as 4amp should be 40mil wide? For the 3amp track would I make this 30mil?

Or is there any other calculations I should be making, like averaging out the current since would the heat be dissipated among the other tracks?

Sorry if this is a stupid question. I've tried to use the search as much as possible but am just struggling with this last bit.

Thanks for taking the time to look at my question.


Joined Jun 6, 2011
The more copper you use, the less power will be dissipated in the tracks.

There is no upper limit (except board space) to the copper you can use, just a lower limit.


Joined Mar 30, 2018
Your diagram of the currents flowing through each section of the PCB tracks is correct – which should allow you to determine the required (minimum) sizing for the currents.