The definition of a confirmed transaction is said to be appr. six blocks after the block with this transaction. But why six blocks? Why not three och eleven blocks?
If I might guess, it’s because the probability of this transaction ending up in a block being rejected is 1/2^6 after six blocks, and that is considered unlikely enough.
I don’t know about the formula but after 6 blocks it is considered as a pretty much irreversible transaction because the chance that you will be in a stale block is very very low. In some wallets you can set it lower or higher depending how much security you want to have.
6x 10 minutes ~ 1h , it is easy for humans to control this period of time in our current time units in our human clocks, so I guess this one of the motives to choose 1h as being the a safe time to wait for a bitcoin transaction.