most people just order standard PCB with 1oz copper. that is 35um thick. in that case for 10A relay traces should be 4mm or wider.
if the relay contacts are used to switch any loads powered by higher voltage such as mains. add U shaped slot in the PCB between low and high voltage:
View attachment 365216

There is no direct "U" slot available in EasyEda it is only rectangle, circle and polygon, so i have created 3 rectangular slots as below, my understanding when we say slot is there will be "U" shaped hole in the board. Is my understanding correct?




I have used 4mm for relay contacts.

 

That should be ok for the slots.

OK, my point about track width was too general You want wide tracks to carry current. At the same time, you want clearance between tracks to prevent possible arcing.

 

In most SW, for a through hole component you can also place the same (duplicate track) on the reverse side.
In Kicad, you have to turn off 'remove redundant tracks'.