10C temp rise=  35 mils width
30C temp rise= 18 mils width
source: Bishop Graphics reference book (now out of print, I believe)
James
PS: won't a 1/2"trace have some possible heat sinking to whatever
it is connected to?

----------
> From: Tim Crist <tjcrist@CCGATE.HAC.COM>
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Circuit Board Trace thickness
> Date: Tuesday, August 26, 1997 2:51 AM
>
>      Can anyone tell me what is the minimum thickness for a 1/2 ounce
>      copper trace on FR4 would be to carry 1 amp continuous?  FWIW, the
>      trace would be about 1/2" long.  I would also be interested in the
>      souce of such information.
>
>      TIA,
>
>      Tim