I live in an area where power-cuts or internet disconnections of ~5 minutes duration are common every couple of week or so. I'm planning to get a 6 GPU (RX470) mining rig for ethereum. If the electricity or internet connection will go out for 2 to 5 minutes once in a week or so, how much can I expect to lose?
If you want an answer in percents, it is quite easy. Assuming that you are mining 24/24 7/7, and assuming you have a battery so you do not need to reboot each time you have an electricity cut, then you will loose:
5/(60*24*7) = 0.000496032 which is approximately 0.05%.
If you want to know how much in ether, you will have to compute how much you expect to mine and to apply the 0.00049 factor to it. Anyway it should not be significant.
However, note that if you have to restart at each cut, it may cost you more.