i have been reading about how Copper weight/thickness is important in several areas of PCB design. The thickness and width of a trace determines the amount of current (amps) the trace can carry. The thickness is also used in the calculation of trace impedance (ohms) in RF and high speed digital circuits however i have yet to find numbers or at least a simple chart that explains the amount of current per copper weight ( kind of like the 40mils per amp rule)

For example how much more current can my 40mils track carry at 1 oz vs 6 oz copper weight?

also, i have yet to se a track burn itself down by the excess current, i have been using the 40mils rule always, how can i be sure o make my pcb safe enough to carry up to 8 amps without using 320mils tracks? (lets assume im limited to 200mils)

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    \$\begingroup\$ The weight increases the height of the copper linearly. If you really can find 6 oz PCB's, they can carry 6x more amps than 1 oz. I don't have any experience with currents over 2A, and I have never used a board with > 1 oz coppery. In addition to self-heating, you might need to consider voltage drop and power loss if it is a low voltage. For example, if it is a 1V supply for CPU core, you might run into practical voltage drop limits before you run into problems caused by trace heating. \$\endgroup\$
    – user57037
    Commented Dec 22, 2014 at 23:27
  • \$\begingroup\$ Play with this circuitcalculator.com/wordpress/2006/01/31/… or this circuitcalculator.com/wordpress/2006/01/24/… to name some... \$\endgroup\$
    – GR Tech
    Commented Dec 23, 2014 at 8:36

2 Answers 2


I always use this website to calculate current carrying capacity.



I can't speak to your specific requirements but I can say that I designed a board with 8 mil traces that carried VCC @ 12V. While testing the board I accidentally shorted the trace to ground and had the board delaminate - literally the traces turned black and burned off the board. It took a while to figure out what on earth was going on because as soon as a small bit burned it acted as a fuse.

So, that's what happens when too much current goes through a trace - it melts.


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