Why was 21 million coins chose as the total number of bitcoins?

[CtrlAltBernanke420]

Why not 1 bitcoin…

Why not 1million or 100million bitcoins, why not 21 billion, or trillion?

Why not 14 million?

[Lauda]

Because Satoshi thought that 21 million is ideal.
Who are we to say that it is not?

[Indefinitely]

As a play on the ridiculousness of the legal age to drink alcohol being 21, while the legal age to sacrifice your life and finally becoming an adult is 18.

[bitspill]

21 million was not chosen, 21 million is the result of multiple other choices.

Initial block reward was 50BTC
1 block is made every 10 minutes
Block reward halves every 4 years

Those three choices lead to 21 million coins, after so many halvings the block reward eventually hits 0 and at that time the number of coins generated happens to be just under 21 million.

[bitspill]

As a play on the ridiculousness of the legal age to drink alcohol being 21

Legal drinking age is 18 in many European countries.

[AgentofCoin]

The answer to the universe and everything is 42.
Since we are human, imperfect, and not God, and only know half of everything, we should use half of 42.
Therefore, 21 million coins represents that half of the great work is done. 

[harrymmmm]

Why not 1 bitcoin…

Why not 1million or 100million bitcoins, why not 21 billion, or trillion?

Why not 14 million?

It's not quite as arbitrary as it seems...
The final total of the infinite series is twice the number issued in the first 4 years (before the first halving). That, in turn, is determined completely by the initial block reward (and the 10 min block time).

So once satoshi had decided on the mechanism and issuance rate, the only parameter left to play with was the initial block reward of 50 btc.

Total of 1 btc would mean there's only 10^8 units (satoshis) to handle the whole system ... not enough.

50 per block probably seemed like a good number to get them mined, distributed, enough to play with even if one only mined one block, etc.

I'm guessing about it tho...someone correct me if i'm missing a good reason here.

[bitkilo]

How did other coins like doge and NXT .ect work out there total coins?

[finnile]

How did other coins like doge and NXT .ect work out there total coins?

They usually estimate how many coins will be mined, and what will be the time by which they all will be mined.Blockrewards/blocktime etc and all taken into account to come to a number.

[Icardi09]

Satoshi think it's ideal
kidding, that number is from mining reward after halving several times in next hundred years.

[Enzyme]

Why not 1 bitcoin…

Why not 1million or 100million bitcoins, why not 21 billion, or trillion?

Why not 14 million?

Satoshi wanted Bitcoin to be rare, it's as if he knew the price boom would happen.

[nikona]

Why not 1 bitcoin…

Why not 1million or 100million bitcoins, why not 21 billion, or trillion?

Why not 14 million?

Satoshi wanted Bitcoin to be rare, it's as if he knew the price boom would happen.

I guess it was a complete accident..n randomly he got to that amount..when he though 21 mil was enough.

[R2D221]

The answer to the universe and everything is 42.
Since we are human, imperfect, and not God, and only know half of everything, we should use half of 42.
Therefore, 21 million coins represents that half of the great work is done. 

If somebody knew half of everything today, they could pretty much become God.

[slacknation]

21 million was not chosen, 21 million is the result of multiple other choices.

Initial block reward was 50BTC
1 block is made every 10 minutes
Block reward halves every 4 years

Those three choices lead to 21 million coins, after so many halvings the block reward eventually hits 0 and at that time the number of coins generated happens to be just under 21 million.

if you look into the source code, 21m was hardcoded, not derived as you have mentioned

[Kazimir]

21 million was not chosen, 21 million is the result of multiple other choices.

Initial block reward was 50BTC
1 block is made every 10 minutes
Block reward halves every 4 years

Those three choices lead to 21 million coins, after so many halvings the block reward eventually hits 0 and at that time the number of coins generated happens to be just under 21 million.

if you look into the source code, 21m was hardcoded, not derived as you have mentioned

Oh, where is that?

Only thing that's hardcoded is:

1. the initial 50 BTC per block
2. reward halving every 210000 blocks

Just these two factors implicitly determine the 21M limit (or actually: 20999999.9769 BTC).

[escrow.ms]

http://bitcoin.stackexchange.com/questions/8439/why-was-21-million-picked-as-the-number-of-bitcoins-to-be-created

Maybe this?

[LiteCoinGuy]

roughly 21x21x21 m



A total of 174,100 tonnes of gold have been mined in human history, according to GFMS as of 2012. This is roughly equivalent to 5.6 billion troy ounces or, in terms of volume, about 9261 m3, or a cube 21.0 m on a side.

Since Bitcoin is often compared to gold, total number of bitcoins matches total amount of gold mined in human history which can be imagined as a cube 21 m on a side.

[runpaint]

Only thing that's hardcoded is:

1. the initial 50 BTC per block
2. reward halving every 210000 blocks

Just these two factors implicitly determine the 21M limit (or actually: 20999999.9769 BTC).

Yes, but WHY?

The block reward doesn't continue to halve forever.  It stops, instead of going to .5, .25, .12, .06, .03, etc.

The correct answer is that Bitcoin was designed to have enough divisible units (Satoshis) to replace the entire money supply of the world.  Obviously it was a rough estimate, but the intent was that 21 million * 100 million Satoshis = enough units to replace all fiat money.

[DannyHamilton]

21 million was not chosen, 21 million is the result of multiple other choices.

Initial block reward was 50BTC
1 block is made every 10 minutes
Block reward halves every 4 years

Those three choices lead to 21 million coins, after so many halvings the block reward eventually hits 0 and at that time the number of coins generated happens to be just under 21 million.

if you look into the source code, 21m was hardcoded, not derived as you have mentioned

Looks derived exactly as explained to me (except that the reward halves every 210000 blocks which is approximately every 4 years):

https://github.com/bitcoin/bitcoin/blob/59310f1c02673c3ee068cd82f8654bed9b757889/src/main.cpp#L1229

Code:

CAmount GetBlockValue(int nHeight, const CAmount& nFees)
{
    CAmount nSubsidy = 50 * COIN;
    int halvings = nHeight / Params().SubsidyHalvingInterval();
    // Force block reward to zero when right shift is undefined.
    if (halvings >= 64)
        return nFees;
    // Subsidy is cut in half every 210,000 blocks which will occur approximately every 4 years.
    nSubsidy >>= halvings;
    return nSubsidy + nFees;
}

[runpaint]

21 million was the intended number, it isn't "derived" in the sense that it's an arbitrary number.  It was coded intentionally to produce 21 million.