How to decided a trace width?

A few gerber that we recieved,the trace width was not enough to build,many engineers unsure how to set up the trace width.

Width is regularly decided by the current signal carries,for a minimum width RCYPCB would recommend more than 4mil,if you have to design any fineline in PCB,you can set the finelins down to 3mil,but please try to set the trace width as bigger as you can. The bigger trace width is helpful smooth production,the fineline will cause higher failure rate in manufacture and higher costs in purchasing.

For the thin trace width,you can add teardrops to the connections of tracks and pads.Teardrops are useful for high voltage/amperage traces.

Anyway,PCB layout practice is a difficult subject to talk about because there are so many  rules, regulations and standards ,so please comply with the different rules, regulations and standards when you design different PCB.