user16: I'm curious, since the inception of bitcoin, what is the average size (in bytes) of a bitcoin transaction?  
To be clear, the easiest way to find this is not to take the size of the block-chain and divide it by the total number of transactions.  This is because there is a little overhead associated with block headers.  Transactions need to be accounted for one at a time for this averaging operation.
Has anyone taken the time to analyze this information and, if so, what were the results?  To be clear, I am interested in this answer as the data is stored in uncompressed-bytes.  I'm not interested in any textual (i.e. JSON) variation which might be used for network communication.

user31233: According to tradeblock.com the average transaction size is about 500-530 bytes

user3041: Just to give a few exact numbers, the current average transaction size (of all existing transactions until block height 498920) is 522.45 bytes.
If we take into account just the first 100000 blocks, then the average transaction size was indeed 238.51 bytes.
This is a plot of the average transaction size (aggregated monthly):

The peak on mid 2015 is produced by this 999657-bytes transaction.
These values can be computed using BlockSci.

user5292: Quote from Gavin Andresen:

the average Bitcoin transaction is about 250 bytes big

https://bitcointalk.org/index.php?topic=813324.0 (2nd post, last sentence)

16: <p>I'm curious, since the inception of bitcoin, what is the average size (in bytes) of a bitcoin transaction?  </p>

<p>To be clear, the easiest way to find this <strong>is not</strong> to take the size of the block-chain and divide it by the total number of transactions.  This is because there is a little overhead associated with block headers.  Transactions need to be accounted for one at a time for this averaging operation.</p>

<p>Has anyone taken the time to analyze this information and, if so, what were the results?  To be clear, I am interested in this answer as the data is stored in uncompressed-bytes.  I'm not interested in any textual (i.e. JSON) variation which might be used for network communication.</p>
 31233: <p>According to <a href="https://tradeblock.com/bitcoin/historical/1h-f-tsize_per_avg-01101" rel="noreferrer">tradeblock.com</a> the average transaction size is about 500-530 bytes</p>
 3041: <p>Just to give a few exact numbers, the current average transaction size (of all existing transactions until block height 498920) is 522.45 bytes.</p>

<p>If we take into account just the first 100000 blocks, then the average transaction size was indeed 238.51 bytes.</p>

<p>This is a plot of the average transaction size (aggregated monthly):
<a href="https://i.stack.imgur.com/ZfVn6.png" rel="noreferrer"><img src="https://i.stack.imgur.com/ZfVn6.png" alt="enter image description here"></a></p>

<p>The peak on mid 2015 is produced by <a href="https://blockchain.info/tx/bb41a757f405890fb0f5856228e23b715702d714d59bf2b1feb70d8b2b4e3e08" rel="noreferrer">this 999657-bytes transaction</a>.</p>

<p>These values can be computed using <a href="https://citp.github.io/BlockSci/" rel="noreferrer">BlockSci</a>.</p>
 5292: <p>Quote from Gavin Andresen:</p>

<blockquote>
  <p>the average Bitcoin transaction is about 250 bytes big</p>
</blockquote>

<p><a href="https://bitcointalk.org/index.php?topic=813324.0" rel="noreferrer">https://bitcointalk.org/index.php?topic=813324.0</a> (2nd post, last sentence)</p>
