A solo Bitcoin miner with an average hashing power of just 10 TH/s (terahashes per second) won the race to add block 772,793 to the Bitcoin blockchain on Friday.

At the time the block was added, Bitcoin’s total hash rate was just over 269 exahash per second, meaning the solo miner’s 10 TH/s hash rate represented just 0.000000037% of the blockchain’s entire computational power.

Put simply: It was an extremely unlikely win for an individual miner.

Despite the odds stacked against them, the solo miner was the first to produce a valid hash for the block to be mined. In return, the miner received 98% of the total 6.35939231 BTC allotted for the block reward and fees. The remaining 2% went to Solo CK Pool, an online mining service that facilitates individual mining.

## Bitcoin’s randomness and probabilities coded for luck and work

To add a block to a proof-of-work blockchain like Bitcoin, the miner must be the first to calculate a valid hash for the block, which can only be discovered using brute computational force.

Mining machines run an encryption algorithm to produce a hash that falls below a threshold specified by the network. If the algorithm produces a value that is above the hash target, the miner tries the algorithm again with a slightly altered input to produce a completely new value for the hash. Miners built specifically to perform this function are able to compute trillions of unique hashes each second.

However, even if a miner’s machine were able to only produce one hash per second, it is theoretically possible that the algorithm’s first output could be a valid hash to solve the block.

## What were the odds?

The chances of adding a block as a solo miner are determined by the number of hashes the miner’s rig is computing per second in relation to the total number of hashes that all of the machines on the network are computing each second.

According to a post from user Willi9974 on the BitcoinTalk forum less than an hour after block 772,793 was solved, the lucky solo miner had an average hash rate over the previous hour of 10.6 TH/s.

The information posted on BitcoinTalk also revealed that the ~10 TH/s was the combined power of four machines (called “workers”). This suggests that this solo miner’s rig was likely made up of four USB stick Bitcoin miners, which can individually achieve a hash rate of around 3 TH/s and cost roughly $200 each.

Using the difficulty level included in block 772,793 and assuming the solo miner’s rig was computing 10 TH/s, it is possible to calculate the total estimated hash rate as 269,082,950 TH/s at the time the block was solved.

Based on this, the odds of this solo miner being the first to solve the block with a valid hash are one in 26.9 million. Statistically, that means that if the same circumstances were repeated infinite times, the solo miner would add the block 0.000000037% of the time, on average.

## Unlikely, but not impossible—and this has happened before

While this scenario was extremely unlikely, similar “once-in-a-lifetime” events in Bitcoin mining have happened before.

One year ago, in less than two weeks, there were three different solo miners that solved blocks with improbable hash rates—the third’s hash rate was apparently just 8.3 TH/s in comparison to the estimated 190,719,350 TH/s total hash rate, which comes out to a one in 23 million chance (or 0.000000044%).

A hash is either valid and thus solves the block, or it isn’t. There is no strategy involved, as the entire system is based on the random generation of hash values and the response mechanisms of the network to maintain core probabilities. Bitcoin runs on code and formulas, so a solo miner somehow solving the next four blocks is perfectly possible within Bitcoin’s mathematical system.

## Mining pools remain the usual winners

Anecdotes about solo miners like these could end up introducing a new hobby to the ever-hopeful. However, the vast majority of blocks added to the Bitcoin blockchain today have been produced by large pools of mining rigs that combine their hashing power and share earnings.

In doing so, each miner’s contribution is rewarded proportionally each time the pool mines a block.

According to blockchain explorer and mining pool BTC.com, the largest Bitcoin mining pool is currently Foundry USA, with its collective 90.19 EH/s computing power making up 31.3% of the network’s total hash rate—which means they earn a share of the block rewards and fees for one in every three blocks, on average.

Mining pools date back to 2010 and have steadily captured greater shares of hash rate distribution year over year as mining difficulty increased and mining technology improved. Today, at least 98% of Bitcoin miners online belong to a mining pool.