Miners are getting paid for their work as auditors. They are doing the work of verifying previous Bitcoin transactions. This convention is meant to keep Bitcoin users honest and was conceived by Bitcoin’s founder, Satoshi Nakamoto. By verifying transactions, miners are helping to prevent the “double-spending problem.”
Double spending means, as the name suggests, that a Bitcoin user is illicitly spending the same money twice. With physical currency, this isn’t an issue: Once you hand someone a greenback $20 bill to buy a bottle of vodka, you no longer have it, so there’s no danger you could use that same $20 to buy lotto tickets next door. With digital currency, however, as the Investopedia dictionary explains, “there is a risk that the holder could make a copy of the digital token and send it to a merchant or another party while retaining the original.”
Let’s say you had one legit $20 and one really good photocopy of that same $20. If someone were to try to spend both the real bill and the fake one, someone who took the trouble of looking at both of the bills’ serial numbers would see that they were the same number, and thus one of them had to be false. What a Bitcoin miner does is analogous to that–they check transactions to make sure that users have not illegitimately tried to spend the same Bitcoin twice. This isn’t a perfect analogy–we’ll explain in more detail below.
Once a miner has verified 1 MB (megabyte) worth of Bitcoin transactions, they are eligible to win the 12.5 BTC. The 1 MB limit was set by Satoshi Nakamoto, and is a matter of controversy, as some miners believe the block size should be increased to accommodate more data.
Note that I said that verifying 1 MB worth of transactions makes a coin miner eligible to earn Bitcoin–not everyone who verifies transactions will get paid out.
1MB of transactions can theoretically be as small as one transaction (though this is not at all common) or several thousand. It depends on how much data the transactions take up.
So after all that work of verifying transactions, I might still not get any Bitcoin for it?
That is correct.
To earn Bitcoin, you need to meet two conditions. One is a matter of effort; one is a matter of luck.
1) You have to verify ~1MB worth of transactions. This is the easy part.
2) You have to be the first miner to arrive at the right answer to a numeric problem. This process is also known as proof of work.
What do you mean, “the right answer to a numeric problem”?
The good news: No advanced math or computation is involved. You may have heard that miners are solving difficult mathematical problems—that’s not true at all. What they’re actually doing is trying to be the first miner to come up with a 64-digit hexadecimal number (a “hash”) that is less than or equal to the target hash. It’s basically guesswork.
The bad news: Because it’s guesswork, you need a lot of computing power to get there first. To mine successfully, you need to have a high “hash rate,” which is measured in terms of megahashes per second (MH/s), gigahashes per second (GH/s), and terahashes per second (TH/s).
That is a great many hashes.
If you want to estimate how much Bitcoin you could mine with your mining rig’s hash rate, we offer a helpful calculator.