Bitcoin Forum

Why was 21 million the number of bitcoins to be created?

 I think Satoshi pulled a random number from his derriere.  :D

I always wondered this myself. Why 21? Is creator of bitcoin fond of blackjack or something? This number has some hidden meaning or it is pure random... I guess we will never know for sure unless someone will found a source.

It is just an arbitrary number. The point is to set a limit.

Because that's how the mathematics worked out.

More specifically, it isn't 21 million.  It's actually 20999999.9769.  It's just easier for everyone to remember and say "There will never be more than 21 million created" than is is to say, "The maximum that could potentially have been created is twenty million nine hundred ninety-nine thousand nine hundred ninety-nine and nine thousand seven hundred sixty-nine ten-thousandths".

What Satoshi actually did was choose a reasonable sounding number 50 and decide that the block reward would be 50 bitcoins per block for the first 210,000 blocks.  Then he decided that in order to have a fixed quantity, but not have a sudden drop off, the block reward would be cut in half every 210,000 blocks.  If you do this cutting in half and adding up all the blocks (rounding down to the nearest satoshi value every time), you'll find that the exact amount of bitcoins that are created by the time the 6,930,000 the block is created is 20999999.9769

every 210 000 blocks the reward is halved

and there is a total of 21 million coins

it has to have a meaning

21 is half of 42
42 is Answer to the Ultimate Question of Life, the Universe, and Everything

Block difficulty is adjusted so that blocks occur on average every 10 minutes.

10 minutes X 210,000 blocks = 2,100,000 minutes.

2,100,000 minutes / 1,440 minutes per day = 1458.333 days.

1458.3333 days / 365.242 days per year = 3.99 years.

It looks to me like he started by deciding that the block reward would be cut in half every 4 years, and then calculated that out to discover it would be 210,379.392 blocks.  Then he probably just rounded off to 210,000.

As far as I can tell, the unexplained magic constants in the bitcoin protocol are:

• Starting subsidy of 5,000,000,000 integer units
• A Bitcoin defined as 100,000,000 integer units
• Subsidy reduced by bit shift (essentially divide by 2 and round down to nearest integer unit)
• Subsidy reduced every 4 years, rounded to be exactly 210,000 blocks
• Difficulty adjusted every 2 weeks (2016 blocks)
• Difficulty adjusted for average 10 minutes per block

I see a lot of numbers in there, but not many 21s.

Very interesting, I didnt know about how it wasn't 21 million exactly.

21 million because it pays to be rich! lol idk but honestly....

it is because 21 million has a significant number, the legal drinking age in most states of U.S.A. Satoshi is also my uncle.

Only the God knows why.If it were unlimited then may be it wouldn't have got any value.Mysteries is what this world is full of

arbitrary number i guess, or maybe he started from the block value, so why 50?

well, 21 is one of the perfect numbers


this is also interesting



Source
http://www.ridingthebeast.com/numbers/nu21.php

There's also the fact that 21 million is within an order of magnitude of the maximum number (67,108,863.99999999) that can be precisely represented to 8 decimal places in double-precision floating-point format. That's probably not a coincidence.

Some people look for conspiracy theories behind every simple thing.

Isn't it a completely arbitrary number?  ::)

This is something that always had me wondering, why was it 21? If I didn't know for sure or had not seen replies in this thread I would be certain that the reason was just a random number he chose. Never heard of any conspiracy theories myself however I agree there is always someone making a conspiracy theory out of something.

6 blocks per hour
* 24 hours per day
* 365 days per year
* 4 years per cycle
= 210,240
~= 210,000
Sum all the block reward sizes:

50 + 25 + 12.5 + 6.25 + 3.125 + ... = 100
Multiply the two:

210,000 * 100 = 21 million

 :)

I think it's difficult to say since no one here actually created Bitcoin.

Because it had to  some number.

Why you shirt is black/white/wharever color, and why it is 12:42:26 when I made this post?

Is there any hidden stuff about these facts?

because there are totally 210000  tons of gold on earth
100BTC == 1 ton of gold  :D :D :D

May be Nokamoto created or thought of bitcoin while he was 21 years old.That's is unknown mystery

thanks a lot, DannyHamilton

:D nice ,BTC is digital golden !!!

If the number of coins was any different, would bitcoin have been less popular/more problematic?
I guess not!

if true 21 million BTC is now circulating in the world, then maybe the BTC will be the number one crypto currencies in the world, because a lot of the wear BTC, it could have an impact on the exchange rate of BTC which will further increase, hopefully this will soon happen ...  ::)

Yeah, BTC is the new gold.

Maybe it is more simple that you would like it to be. It is just a good number of 21 and million is just because many had atleast 1 BTC :)

BTC is probably digital gold 2.0  :)

True, but as Danny mentioned, the choices of these "magic constants" are still unexplained.
Why was the block time set at 10 minutes not 5? Why was the block reward set at 50 btc not 100? etc.

Yeah it's effectively an amount that Satoshi deemed appropriate. He had to consider block-halving times and thus the slow fading-out of block rewards for miners, in transition to transaction fees that 'pay' the miners.