According to Coinbase director Conor Grogan, a total of 913,111 Ethereum (ETH) tokens are "lost forever" due to user error. The above-mentioned figure represents 0.76% of the entire ETH supply. 

At current prices, a total of $3.4 billion worth of ETH has been lost.

Such user errors might include mistakenly sending ETH to non-recoverable addresses, smart contract mistakes or failed multisig wallets. 

For instance, the Parity wallet, which was used by the Web3 Foundation, implemented multisig functionality, but the contract that governed access to these funds was destroyed. Roughly 306,000 ETH ($95 million at the time) ended up being frozen. No hard fork was released in the aftermath of the incident, and the frozen funds are still visible on-chain.

The now-defunct Canadian crypto exchange QuadrigaCX had stored around 60,000 ETH in wallets that were not properly documented. Some of its ETH was reportedly sent to incorrect smart contracts.

In 2022, the Akutars NFT project, which was initiated by former MLB player Micah Johnson,  ran a Dutch auction mint for its non-fungible token (NFT) collection. However, two key smart contract bugs caused a disaster, with $34 million ending up being unrecoverable.

Thousands of users have also sent ETH to burn or null addresses due to typos in address inputs or other reasons. According to Grogan, 25,000 ETH have been collectively sent to burn addresses.

That said, he also admits that the $3.4 billion likely undershoots the actual amount of lost ETH. Notably, the amount does not cover lost private keys.

At the same time, roughly 5.3 million ETH tokens have been burned following EIP‑1559, which was introduced during the London hard fork in 2021.