How many confirmations make a transfer safe?
One confirmation is usually enough, until it is not. What a confirmation actually proves, why services wait for several, and how the number differs per chain.
A confirmation means your transaction is in a block, and that block is part of the chain everyone agrees on. Each additional block on top is another confirmation.
More confirmations means more work would have to be redone to reverse it, which is why a bigger number means safer rather than just newer.
Why one is not always enough
Occasionally two valid blocks appear at nearly the same moment and the network briefly disagrees about which is the real one. The losing block's transactions go back into the queue.
In practice this resolves within a block or two, so a transaction several blocks deep is settled for any ordinary purpose.
Typical thresholds
Bitcoin: most services want 2 to 6 confirmations, which is roughly 20 to 60 minutes. The high end is for large amounts.
Ethereum: 12 or more blocks is common, which is a couple of minutes.
Tron: around 19 blocks, which at three seconds a block is about a minute.
Note that these are not comparable as raw numbers. Six Bitcoin confirmations represent an hour of work; nineteen Tron confirmations represent a minute. The number reflects each chain's own block rate and finality model.
What this means while you wait
A transfer showing one confirmation has almost certainly succeeded. If a service has not credited it yet, it is applying its own threshold rather than doubting you.
Check the count on the explorer for your network. Once it is past the threshold and still not credited, that is the point to ask a human, with the transaction ID in hand.