There is no such thing as 100 percent safe ice.
The Iowa Department of Natural Resources recommends a minimum of four inches of quality ice for fishing and at least five inches for snowmobiles and ATVs.
Ice thickness is not uniform on any body of water. Things like current and springs slow ice growth. Rocks, trees or docks that poke through the ice like will conduct heat and make the ice around it less stable.
There could be pockets of thin ice or places where ice recently formed, so it would be wise to check ice thickness as you go out.
The insulating effect of snow slows down the freezing process.
Safety items in the bucket: Ice picks, about 50 feet of rope and a throwable floatation seat cushion for use in case of rescue.
Ice fishing is a social activity, don't go out alone. If the worst should happen, someone would be there to call for help or to rescue.
Avoid off-colored snow or ice. It is usually a sign of weakness.
Trust your instincts. If it doesn't look right, stay off.