Conditions are so variable, that it’s difficult to come up with a reliable benchmark. Water flow and temperature under the ice, the way the ice forms, and other things can make it hard to determine how hard and supportive the ice will be. It is often not uniform from area to area on the same water body, as well.
If you want to try it, have redundant safety measures. When I would go out on untested ice, I would over dress in synthetics, to lessen the shock if I went in. A small dry bag backpack, full of a change of clothes to be thrown to solid ice, a couple of pointy screwdrivers joined by a piece of cord in a front pocket of my outer layer to pull my way out of the water, and if it seemed really dicey, a friend on shore with a throw bag like you use for river rescue. Stay close to shore to begin with. Poke like that guy did to check the thickness. I have gone without trouble on 2" of ice, and have also broken through on the same thickness on another pond. The element of the unknown adds to the fun, but none of it is worth your life, so just use your head so you don’t get in over your head.
