user3763: Okay, my hard drive is a bit cramped, and the Blockchain for my Bitcoin client is completely sucking up my free space. I want to know how much room I need to be prepared to lose.
This isn't a duplicate of the other questions - those had answers that were highly impractical - I'm not sure if they dealt more with the theory of the blockchain or what, but the filesizes were way off.
For example, right now, http://blockchain.info/charts/blocks-size says that the current blockchain size is 6073 MB, which is complete BS - the cumulative size of ~/.bitcoin/blocks/*.dat is 6970 MB, and it's not even done yet.
Basically, what I want is a realistic, down-to-earth estimate of how much hard disk space the blockchain is going to cost me. Not the theory, not the "data minus overhead", the actual cost of the .dat files.

user3439: On my Mac, the blocks directory consumes 7.8 GB of physical space. The entire Application Support folder takes 8.0GB. 
For those not familiar with Macs, the Application Support folder is somewhat like a hidden data folder. It is where applications keep their data other than the documents users actually work with. (Which are usually in the Documents directory.) It is where the Qt client keeps both the blockchain, address book, wallet, and other databases.

user54391: As of July 12th 2017 a full node running on my machine requires 130 GB of disk space:
$ du -s ./bitcoin-data
136467234   bitcoin-data

I have the txindex option enabled (txindex=1 in bitcoin.conf) so the above includes 11.5 GB of optional transaction index data, this is not enabled by default.
The size of just the block data is 116.29 GB and the chain state is 2.33 GB.
If you do not have enough free disk space you can run Bitcoin with pruning enabled, this will delete old block files, set prune=550 in bitcoin.conf (550 is the minimal value) and it will automatically prune the block data to stay under 550 MB. 
This makes the actual size with pruning enabled around 2.86 GB (block data + chain state).

user11997: The blockchain sizes of Bitcoin, Litecoin, Dash, Dogecoin, Peercoin and Namecoin are listed here at https://bitinfocharts.com/
(scroll down to Blockchain Size)
As of today (2015-07-12) the sizes are (sorted by market capitalization):
Bitcoin             Litecoin          Dash              Dogecoin          Peercoin          Namecoin
44.73 GB            4.64 GB           1.01 GB           11.41 GB          0.4191 GB         2.64 GB
$4,477,078,707 USD  $209,054,841 USD  $23,217,866 USD   $20,686,200 USD   $15,897,328 USD   $9,888,883 USD

Note that Dogecoin, although very new, has a very big chain already, where Peercoin has by far the smallest.
Your question
On my hard disk the .bitcoin directory uses 45 GiB = 48 GB.

3763: <p>Okay, my hard drive is a bit cramped, and the Blockchain for my Bitcoin client is completely sucking up my free space. I want to know how much room I need to be prepared to lose.</p>

<p>This isn't a duplicate of the other questions - those had answers that were highly impractical - I'm not sure if they dealt more with the <em>theory</em> of the blockchain or what, but the filesizes were way off.</p>

<p>For example, right now, <a href="http://blockchain.info/charts/blocks-size">http://blockchain.info/charts/blocks-size</a> says that the current blockchain size is 6073 MB, which is complete BS - the cumulative size of <code>~/.bitcoin/blocks/*.dat</code> is 6970 MB, and it's not even done yet.</p>

<p>Basically, what I want is a realistic, down-to-earth estimate of how much hard disk space the blockchain is going to cost me. Not the theory, not the "data minus overhead", the <em>actual</em> cost of the .dat files.</p>
 3439: <p>On my Mac, the blocks directory consumes 7.8 GB of physical space. The entire Application Support folder takes 8.0GB. </p>

<p>For those not familiar with Macs, the Application Support folder is somewhat like a hidden data folder. It is where applications keep their data other than the documents users actually work with. (Which are usually in the Documents directory.) It is where the Qt client keeps both the blockchain, address book, wallet, and other databases.</p>
 54391: <p>As of <strong>July 12th 2017</strong> a full node running on my machine requires <strong>130 GB</strong> of disk space:</p>

<pre><code>$ du -s ./bitcoin-data
136467234   bitcoin-data
</code></pre>

<p>I have the txindex option enabled (txindex=1 in bitcoin.conf) so the above includes <strong>11.5 GB</strong> of <strong>optional</strong> transaction index data, this is not enabled by default.</p>

<p>The size of just the block data is <strong>116.29 GB</strong> and the chain state is <strong>2.33 GB</strong>.</p>

<p>If you do not have enough free disk space you can run Bitcoin with pruning enabled, this will delete old block files, set prune=550 in bitcoin.conf (550 is the minimal value) and it will automatically prune the block data to stay under 550 MB. </p>

<p>This makes the <strong>actual size with pruning enabled</strong> around <strong>2.86 GB</strong> (block data + chain state).</p>
 11997: <p>The blockchain sizes of <strong>Bitcoin</strong>, <strong>Litecoin</strong>, <strong>Dash</strong>, <strong>Dogecoin</strong>, <strong>Peercoin</strong> and <strong>Namecoin</strong> are listed <a href="https://bitinfocharts.com/">here at https://bitinfocharts.com/</a>
(scroll down to <em>Blockchain Size</em>)</p>

<p>As of today (2015-07-12) the sizes are (sorted by market capitalization):</p>

<pre><code>Bitcoin             Litecoin          Dash              Dogecoin          Peercoin          Namecoin
44.73 GB            4.64 GB           1.01 GB           11.41 GB          0.4191 GB         2.64 GB
$4,477,078,707 USD  $209,054,841 USD  $23,217,866 USD   $20,686,200 USD   $15,897,328 USD   $9,888,883 USD
</code></pre>

<p>Note that Dogecoin, although very new, has a very big chain already, where Peercoin has by far the smallest.</p>

<h1>Your question</h1>

<p>On my hard disk the <code>.bitcoin</code> directory uses 45 <a href="https://en.wikipedia.org/wiki/Binary_prefix#IEC_standard_prefixes">GiB</a> = 48 GB.</p>
