I'd like to build up my own digital archive, probably a NAS or something like this. But I have to estimate the required storage capacity, before planning and buying it.

Is there a comfortable way to determine the total amount of all the downloads in my library? I don't want to check this for all my games and its downloads (installer + extras) individually. Maybe there is a database like steamdb.info for GOG, which allows querying download sizes via rest api or rdf?

Thanks for your answer. Gogrepo seems very helpful for my case, I will examine it. But still I'd like to know, how much it would take before, because I do not want to buy 8 TB, when I only need 2 TB, or start with 2 TB and have to upgrade to more directly after that.

Of course I will consider all of my data (and planned future stuff) and fault security. But thank you for mentioning it.

MaGog is probably the easiest way actually. If you follow the instructions to import your games list you can then filter by owned games and it will give you a total size for all games. It won't include bonuses or extras and it's only a rough estimate but it's a start.

I was about to suggest the same thing I just noticed adalia suggested, so count that as a +1 for adalia. :) In addition to that however, I own approximately 548 or so GOG games in my library, however that number is the "unbundled" count and not equal to the number of actual products purchased which would be smaller than that, probably around 450 or so. I have downloaded all of the Windows-only English-only installers, all of the bonus goodies for all my games. The only things I have not downloaded are:

- non-English game installers and goodies
- non-Windows game installers and extras installers
- For games that provide the soundtrack in FLAC and MP3 format, I only download the FLAC format since MP3 is redundant and could be generated from the FLAC files.

My entire game collection is 1,022GB, and includes one copy of the complete Witcher 3 GOTY with extras, and every major copy of the original game and all extras plus the patches to be able to patch it up from the original release to any subsequent version, which consumes about 200GB of that total. If I discarded my historical archive of the game, and just kept the most recent GOTY+extras I'd shave about 150GB off my total archive, bringing it down to about 850GB.

I own approximately 1/4 of the GOG game catalogue, and the total size in gigabytes appears to be approximately 200% as many as the store shelf product count, or approximately 180% of the game library count in gigabytes. One could use this as a very crude estimate and say that if you owned 1000 games in-library, it would take up 180% or 1.8GB. Of course this would vary wildly depending on how a particular person's game collection compares to the average sizes of games in my collection.

Other than my ballpark figures and the suggestion adalia gave though, I think the only more accurate way you could determine a number is to download all of the files you want to archive and measure how much space they take up. That will vary further based on whether or not you download just single languages or all of them, just a single OS installer or more than one, etc.

Oh, one more thing - my estimates are for standalone installers which do NOT contain GOG Galaxy. I have no idea how much larger the recent Galaxy inclusion in various standalone installers may have bloated them out, but it could be anywhere from a few megabytes if it is a stub installer that downloads everything, to 150MB or so per game if they included the entire kitchen sink. You'd have to adjust the estimates accordingly based on that as well.

Thanks to @nightcraw1er.488 i tried out gogrepo. After creating the manifest with gogrepo update I can simulate downloading my library using gogrepo download -dryrun. This ends with the log line 493.71GB left to download.