Many people go on 2" thick ice but I don't feel confident about that. 3" is much better. If it's 4" then you don't have to worry about anything even if your weight is above average.
You should remember that ice thickness varies in different places. Under snow it can be thinner. Be careful in places with current or underwater springs.
There is a great difference between autumn ice and the spring one. Usually it's much stronger in autumn.
