Block Height vs Block Length

Should we standardize our copy around the term “Block height” to denote the number of blocks in the blockchain along the longest path or “Block length”?

It seems like Bitcoin uses block height, but ouroboros uses the term block length.

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Slot length is a distinct separate metric that has another meaning (the slot where a block can be produced in ouroboros)

X-Posting from discord discussion:

imo, they are synonymous, but there is a slightly different conotation with how they are used in the community, it seems. Block length is a parameter of consensus (e.g. “in pow, the longest chain is always selected”). Block height is typically used as a more generic structural property of the blockchain (e.g. “this block is at height X”). Then there is epoch:slot, which for us is the “positional” terminology.

I would want to stick with whatever the rest of the industry uses (which afaik is block height). My logic is what % of people that use the CLI / wallet will have used Bitcoin / Eth vs. what % would have read ourouboros papers? If we imagine the former would be higher, then we should go with that.

Additionally, this thread started in discord due to ssh posting: “And why is one called block length and the other one block height?” So I imagine there may be some confusion if we don’t clearly articulate what the terms are (even if we go w/ block length).

Not that I disagree entirely, but it’s worth mentioning that the notion of “length” is actually a proof of work concept (choosing the “longest” chain). So one does not need to have read Ouroboros to be familiar with it. But I agree that we should stick with what the community wants, externally at minimum.

Ah gotcha - I was thinking one of the main arguments for keeping block length was to remain consistent with the ouroboros papers. Yeah, longest chain is definitely from pow

I don’t think »block length« is a thing. As far as I am concerned, a block is the smallest—or only–unit in a blockchain, ie a thing, that itself has no unit. It can be looked at in relation to other blocks, which would be the hight.
What you are referring to is the chain and not the block, when you talk about length.

Plus, longest chain is not proof of work specific. I think what you mean might be heaviest chain—although even PoS can have a notion of difficulty—?

Two examples: there is an an Ouroboros variant, which also uses the longest chain rule: and Algorand uses longest chain rule.


FWIW, I’ve always followed this terminology…
Chain length - the length of a chain of blocks
Block height - the height of a block, but also commonly refers to the maximum chain length when taken in the context of the blockchain as a whole