3,573,000,000 is the size in bytes of the blockchain
That's not actual size of the chain itself, that is the size of the serialized data structures that get stored by the daemon. This is done somewhat inefficiently. The actual size is roughly half that.
Also, current transactions on the chain are larger than a long-term average would be (with more usage), because of the relatively high portion that are pool payouts, or spending of dusty pool payouts. Once the typical coin is spent around many times rather than being mined and hoarded or spent a few times, the average will converge to something closer to what I estimated above, which is about 8 inputs, 8 outputs, possible somewhat smaller.
I guess that brings us a bit closer.
I think the pools have been stabilized with their payouts for, let's say half their lifetime now, so we're dealing with about a 75% of 50% of 97.6% of 90% of 10315, or about 1132 bytes, which is only about 51% larger than fluffypony explained.
My error was caused the the lack of want to incorporate almost double the amount of time necessary to estimate the size in the first place, resulting in a 10% error.
My second error was caused by apparent lack of incorporating that 1 kb is exactly 1024 bytes and not 1000 bytes, resulting in a ~3% error.
My third error was based on the assumption that the blocks were not based on a database, resulting in a 50% error.
My fourth error was based on that pool payouts were every block, instead of at a certain threshold, which is arguably speculative, resulting in a 75% error.
But the reality is, the acutal blockchain size on my computer right this second is still well over 10kb/tx, regardless of speculative changes or archetypal changes to block structure ........ since april 14 2014 until feb 8 2015, the average transaction size is, in real average reality over 10 kb per transaction.
I understand that a db will mitigate this, and pool payouts will change this, and bytes/kbytes across continents will change this, but the actual size of the file on my computer compared with the real number of people that has made a transaction on the monero network to date, is really 10kb per transaction.
I see that it's not getting bigger, but please, understand that this is a massive number.
it will take time for it to go down, time that I expect will be paid for in whale blood.
I am a holder, a gambler, but not a buyer.