The constants
The beacon chain genesis was on 1 December 2020 at 12:00:23 UTC. Every slot lasts exactly 12 seconds and 32 slots form an epoch, 6.4 minutes. The slot number of any moment is therefore a simple division, and the time of a slot is a multiplication. Execution-layer block numbers are a different counter: a slot without a block (a missed proposal) has no execution block.
slot = floor((unix time โ 1,606,824,023) รท 12)
epoch = floor(slot รท 32)
slot start time = 1,606,824,023 + slot ร 12Finality
Validators vote on epoch boundaries. When two-thirds of the stake agrees, an epoch becomes justified, and the one before it finalized. In normal conditions a transaction is final after about two epochs โ 64 slots, roughly 12.8 minutes. Exchanges that wait for a few dozen block confirmations on Ethereum wait for a similar order of time. Finality can be delayed if many validators are offline.
Where you need it
- Validator duties and rewards: dashboards list slots and epochs for proposals and attestations.
- Withdrawals and exits: queues and sweeps are measured in epochs.
- Debugging timestamps: block.timestamp on Ethereum equals the slot start time of the block's slot.
- Planning upgrades: hard forks activate at a given epoch, and this converter tells you the date.
Frequently asked questions
+How long is an Ethereum epoch?
32 slots ร 12 seconds = 384 seconds, 6.4 minutes.
+When was slot 0?
1 December 2020, 12:00:23 UTC โ the beacon chain genesis (Unix time 1606824023).
+Is the slot number the same as the block number?
No. Block numbers count execution blocks since 2015; slots count 12-second beacon chain intervals since December 2020, and some slots are empty.
+How long until an Ethereum transaction is final?
About two epochs, roughly 12.8 minutes, under normal network conditions.
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