In Ethereum Proof of Stake, how was this particular slot time of 12 seconds decided upon?

Credit: https://old.reddit.com/r/ethereum/comments/gb8j89/eth20_slot_time_a_question/

2 Answers 2


Ethereum slots are 12 seconds to allow a balance between decentralization and finality time.

Basically, all validators must be able to handle work/load/messages within the slot time. Shorter slot times would require validators to be more powerful and lead to less decentralization. Longer slot times would increase the time to finality.

A slot time of 12 seconds was based on benchmarks and an estimate of the maximum number of validators.

Reference: https://notes.ethereum.org/@vbuterin/serenity_design_rationale?type=view#Why-32-ETH-validator-sizes

With a finality time of 2 epochs (2 * 32 * 12 = 768 seconds), that implies a max overhead of (2^22)/768 ≈ 5461 messages per second.

We can tolerate such high overhead due to BLS aggregation reducing the marginal size of each signature to 1 bit and the marginal verification complexity to one elliptic curve addition (see Lighthouse benchmarks).

Credits to 0xTerence Reddit user for the reference.


So, Ethereum slots have a 12-second block time because that's how long it takes for a new block to be added to the blockchain. This block time is set by the Ethereum network protocol to ensure that transactions are processed efficiently and securely. The 12-second block time is a bit of a compromise. It's short enough to keep transactions moving quickly, but long enough to give miners time to verify and add transactions to the blockchain. Now, you might be wondering why this matters for slots. Well, in the world of online gambling, every second counts. A shorter block time means faster transactions, which means less waiting around for your bets to be processed. So, while 12 seconds might seem like a random number, it's a carefully chosen block time that helps keep the Ethereum network running smoothly.

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