I understand you have to download the entire blockchain and sync in the beginning but don't you also have to constantly keep the software on if you want to buy/sell stuff, which means more data being downloaded to my personal comp every instant there is a transaction.

If this is true, what is the average amount of data per month being downloaded so that I can use bitcoin.

Also if this is true, why isn't this point highlighted on bitcoin.org, they say you have to initially download the blockchain but not that its constantly going to be downloading data on your comp, data is expensive!

  • Note that there are plenty of other, so called "thin" clients which are perfectly fine if you just want to use Bitcoin, e.g. to buy/sell stuff. Both mobile (all mobile clients are lightweight) as well as desktop clients (e.g. Multibit or Electrum). Furthermore you can also use web wallets, such as coinpunk.com or blockchain.info/wallet and others. – Madzi Konjo Nov 10 '14 at 6:03
  • First: "data is not expensive" is not really true. Both harddisk and bandwidth are cheap and getting cheaper. But maybe you are in a situation where it's not cheap for you, so there are several solutions for that. – Jannes Nov 10 '14 at 10:58
up vote 1 down vote accepted

At the time of writing, the blockchain is 24 GB in size after 5 years. This is an expansion of 0.12 kilobytes per second. However, this does not represent all of the bandwidth used by the Bitcoin client:

  1. The Bitcoin client also relays transactions and blocks it downloads.
  2. The protocol has overhead.
  3. Sometimes the Bitcoin client will download transactions that don't get into the blockchain.

I tested the amount of bandwidth that Bitcoin uses by measuring it using bwm-ng, over the course of six and a half hours. I found that it uses 2.1 kilobytes per second, combining upload and download. Over a month, that would add up to 5.5 GB.

Note that my Bitcoin client did not accept incoming connections, which would have changed the result significantly.

This can be an expensive amount of bandwidth. In that circumstance, you can use an alternative, like BlockChain.info, or MultiBit, both of which use almost no bandwidth.

  • 2
    The actual download usage of full Bitcoin nodes is somewhat higher because you need to download each transaction twice: once when it is first broadcast and again when it appears in a block. (This needless inefficiency will be fixed in the future.) Also, you download some transactions and other data that doesn't end up in the block chain. Upload bandwidth is much higher than that because you sometimes need to send a transaction or block to each of your peers, and you might even be asked by a peer to send them the entire block chain. – theymos Nov 10 '14 at 4:30
  • @theymos Thanks for the help improving my answer. Could you look at the edit? – Nick ODell Nov 11 '14 at 6:28

You don't need to run the software 24/7, it just needs to be up-to-date in order to use it when you need to use it, to catch up with a few days worth of blockchain data doesn't take long and wont use much bandwidth.

Each block is 1Mb or less (at the moment) and occurs once every 10 minutes (roughly). So block data is fairly negligible in terms of bandwidth used.

However, as a full node you will also be peer-to-peer transmitting and receiving transactions and also supplying historical blocks to out-of-date peers. It's impossible to predict monthly data transfer because it depends on which peers you are connected to, but it's likely to be several gigabytes per month.

There are also other options instead of running a full node, bitcoin.org details these. e.g. blockchain.info, Hive, Xapo, MultiBit, GreenAddress, etc. You could also rent a cheap VPS server to run a full node on and configure your local node to only connect to that which would save a lot of bandwidth by removing the peer-to-peer data.

  • Note that the cheapest VPS servers may not have enough memory or disk to run a full node. Also note that VPS providers often charge for bandwidth, at a rate that may be higher than the OP is paying for home Internet. – Nate Eldredge Nov 10 '14 at 6:35

Another solution (mostly for future readers of these answers) is getting your Bitcoin data from satellite or DVB broadcasts.

DVB project currently piloting in Finland: http://kryptoradio.koodilehto.fi/

BitSat project, under development: https://bitcointalk.org/index.php?topic=334701.0

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