Why Is a 6-Block Confirmation Depth Considered the Standard for Bitcoin Transactions?

A 6-block confirmation depth for Bitcoin is an arbitrary but historically accepted standard that balances security with transaction finality time. It is based on the probabilistic cost of a 51% attack.

With each additional block, the probability of an attacker successfully generating a longer chain and reversing the transaction drops exponentially. After six confirmations, the cost to re-mine the chain becomes astronomically high, making a successful double-spend economically unfeasible for most attackers.