I have fished on ice that was 1in and been safe all day, and went threw ice that was 10in thick. Were I live we get lots of snow so even if it has been cold the snow can keep good ice from forming.

This is what I go by, granted the ice is consistant
3in safe to walk
6in safe for snowmobile
12in safe for Truck

I know some guys that will fish on 3in of slush all day, but not me.

Dont kill you self, ice fishing is not that much fun.