Every few years I look into having an offline copy of wikipedia. Don't know why, just something that feels like I should have. Here's what worked well for me in late 2025.
I started with Kiwix.org, an open-source project designed to make it "easy" to have offline access to websites, including wikipedia, but also many others. They provide apps for Android, iPhone, Windows, etc. I installed the Windows version, via the Microsoft Store. Why the MS Store? Because automatic updates are more transparent.
To view a site offline, the Kiwix app needs an "archive" file with .zim suffix. On first launch, Kiwix asks which .zim archive file I want to open. Since I didn't have any archive files yet, I needed to find a way to download a .zim archive for wikipedia.
The initial Kiwix launch screen has a button for "Open library", which goes online to find potential .zim archive files for download. Using the "Open library" gives a clunky/old-school list of folders, kind of like an old ftp site.
I scrolled down and clicked on "wikipedia". Now I have a huge list of archive files, which one? There is a filter above the list for "language", so I chose "English" which filtered down to "only" a few dozen entries. There is also a "Subject" filter with entries like: top; top1m (top 1 million?); astronomy; baseball; etc. I want "everything", but no option in the "Subject" filter for that. So I sorted on size.
The largest was 111 GB, named wikipedia_en_all_maxi_2025-08.zim. Based on the file name it seems like this is english ("en") with everything ("all_maxi") from Aug 2025 ("2025-08"). The other entries sorted by size had things in name like "all_nopic", so I guess this means no pictures. Or "top1m_maxi", so I guess top 1 million articles with pics.
The largest wikipedia_en_all_maxi_2025-08.zim seemed like what I want, everything with pics. Clicking it offered different download options. It recommended using bittorrent, to be a good citizen. I'm familiar with bittorrent so took that option. I'm sure that the other download options work fine, too.
After the 111 GB download of the .zim archive file finished, I went back into Kiwix app and used "Select storage" to open the .zim archive. And there it was, the full wikipedia, with images, as of Aug 2025.
A few final thoughts…
There are archives for lots more than wikipedia: gutenberg, wikibooks, wikivoyage, and others
Strictly speaking I don't have the full full wikipedia, because the .zim archive I downloaded is only current article body with pics, but does not include things like: full history of each article; discussion (talk) about each article, etc. But that's ok for my needs. I'm sure that getting the full history and discussion would at least double the size, probably more like 10x.
Because I used torrent for download, and keep the torrent running on my side, I'm contributing back to the community for people who want to download.
I will need to periodically get a newer .zim archive of wikipedia. But each time I'll still have the older one around, for reference.
I'm guessing this would also work well with mobile devices, using Kiwix for Android/iPhone. Of course this uses up 100+ GB of storage on the device. But some Android devices, especially "tablets", support microSD cards, which are down to $25 for a 256 GB card. So that's not too bad.