trace size vs. current

Hi, every one
first time trying to build my own board
how do we determine how much current can be past through a given size trace

having problem deciding witch relay to use:
1st relay is 25 amp pcb only.would have to add blade power connecters as close
as passable to the relay. hence the first question.

2nd relay is 25 amp pcb w/blade connecters built in on top. but much larger than 1st.
trying to keep board as small as passable

dose tinning add current rating to trace

Look at wire size... 2.5mm diameter is about 16 amps.. so that is about 8mm square..
For 25 amp I would be putting down 10mm trace minimum... Equivalent to 3.2mm wire..

A google search for PCB trace width calculator brings up a lot of utilities.

hi,
Look at this tutorial pdf, pages 6 & 7

E

dose tinning add current rating to trace

Click to expand...

Some of my "China PCBs" have very thin copper. I have no solder mask over the high current traces and tinning added. This reduces the resistance slightly, helps spread out the heat a little, and the bumpy surface emits heat better.

On thick copper, i think this tinning helps much less.

Hi

Here's a nice free tool...

https://www.saturnpcb.com/pcb_toolkit.htm

eT