12

Miners work on finding blocks but don't sent anything until they find the block.

Considering that, how can sites like bitcoincharts.com display a graph of the network hash rate?

  • 2
    If I flip a fair coin repeatedly, and tell you that I found 1 billion heads, it's (practically) statistically certain that I flipped the coin very nearly 2 billion times. The same sort of extrapolation can determine the total network power based on the success rate. – Tim S. Jan 30 '14 at 21:53
19

The hashrate can be calculated from the expected rate of finding a block (144 a day), the actual rate of finding a block and the current difficulty.

So let's calculate the average hash_rate for a single day:

expected_blocks = 144
difficulty = 11187257.461361 # this is on May 22nd 2013
blocks_found = 155 # Also May 22nd 2013
hash_rate = (blocks_found/expected_blocks*difficulty * 2**32 / 600)

The reason we use a day to average out the hash_rate is that taken block by block the variance would be really high and we would not get anything meaningful.

According to WolframAlpha this gives us an averagge hash_rate for the 22nd May 2013 of 86.19 THashes/s. Numbers of course may vary depending on how you chose your interval, which appears to be the reason numbers don't match with the ones on Blockchain.info

  • I know this answer was given 5 years ago, but why 2**32? I'm presuming it has something to do with the 256-bit hashing function used, but some clarification would be awesome :) – glowkeeper Oct 4 '18 at 13:34
  • 1
    @glowkeeper see bitcoin.stackexchange.com/a/30225/60443 – JBaczuk Nov 14 '18 at 20:39
  • Thanks, @JBaczuk! Looks good! I should probably check that answer against mine (bitcoin.stackexchange.com/questions/79774/…), but I'm currently knee-deep in code, so I'll report back later, once I've done some back-of-the-envelope-calc's :) – glowkeeper Nov 16 '18 at 9:53
8

The network hash rate can be statistically inferred from the difficulty and the rate at which blocks are found. It's just a more complex version of the fact that if you know that someone is flipping coins and heads comes up 800 times an hour, they're flipping about 1,600 coins an hour.

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