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I would like to estimate the total number of hashes (double SHA-256) that have been performed for bitcoin purposes.

As an estimate, I downloaded mining stats, massaged the numbers (assuming the rate shown is for the period ending at the date indicated and starting at the date before), came to 201⋅1024 hashes (equivalently 287.38 or 288.38 SHA-256) on Oct 28, 2017.
[update: 517⋅1024 hashes that is 288.74 or 289.74 SHA-256 by May 4, 2018].

Did I goof badly in that estimation of the hashes used for mining?

What other comparably non-negligible number of hashes is performed for bitcoin purposes, and how can that be estimated?

Clarifying: I'm looking only for things that represent a sizable fraction of the number of hashes spent for mining, say at least 0.5%; I'm totally willing to ignore the rest.

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    The total number of non-mining hashes is many orders of magnitude smaller than the mining hashes; much less than your 0.5%. So in fact you are going to ignore all of them. – Nate Eldredge Oct 27 '17 at 19:41
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Assuming the numbers in the link are correct, then I think this would be right.

I got the same result by multiplying every entry by (1,000,000,000,000 * 3600 * 24 * 2) and adding them up. Came out to 2.008E^26.

But the total number of hashes is much higher. Every block in the blockchain is hashed by every client, every transaction is created using several hashes, etc, etc.

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    Thanks for checking my computations! Isn't it safe to say that the number of hashes performed when "block in the blockchain is hashed by every client" is negligible in comparison? I'm looking at a significant "etc, etc".. Perhaps, for blockchain maintenance/compaction, which remains quite a mystery to me. – fgrieu Oct 27 '17 at 17:04
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    Depends what you consider negligible. A rough Fermi estimation for this number would be for the blockchain (500,000 blocks * 1,000,000 total downloads) = 500,000,000,000 and for transactions (250,000,000,000 * 10,000 clients) = 2,500,000,000,000,000. So small in comparison to the mining hash rate, to be sure, but perhaps not negligible. – Luke Mlsna Oct 27 '17 at 17:12
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    Validating a single block can involve tens or hundreds of thousands of sha256. Every block has a tree of double sha256 leaves, every signature has at least one sha256 possibly multiple. – Anonymous Oct 28 '17 at 4:29
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depending on what you are asking, you might want to include all hashing done on all full nodes as part of the transaction validation as well.

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