This ZIP to 7Z conversion does not run here
7Z is smaller than ZIP, which is why people ask for it.
Browsers cannot create a 7Z file.
What to do instead
Use 7-Zip or PeaZip on your computer. If you have a 7Z and need something everyone can open, use 7Z to ZIP on this site.
The page that does work is 7Z to ZIP.
ZIP to 7Z without the extra promises
ZIP to 7Z sits on this site because ZIP and 7Z are not interchangeable, even when they look similar in a file list. 7Z is smaller than ZIP, which is why people ask for it. ZIP is the file you send when you do not know what the other computer has installed. Downloads use 7Z. The other computer often needs ZIP instead.
Browsers cannot create a 7Z file.
Read this about ZIP before you upload
ZIP is the archive everyone can open. Windows, macOS, and phones all understand it. A ZIP of a PDF is not a meaningful compression of that PDF. Password-protected archives fail.
Keep the original archive until the ZIP has been opened on the other computer.
Read this about 7Z before you send the download
The download has to be 7Z, because that is the format the next step named. Downloads use 7Z. The other computer often needs ZIP instead. This site can unpack 7Z into ZIP.
Very large archives are happier on a computer than a phone. Encrypted archives fail.
Keep, check, then delete
People lose time when they convert before they know which rule failed. Size, pixel dimensions, codec, font encoding, and layout are different rules. ZIP to 7Z only addresses the ZIP to 7Z step. 7Z is smaller than ZIP, which is why people ask for it. Browsers cannot create a 7Z file. Use 7-Zip or PeaZip on your computer. If you have a 7Z and need something everyone can open, use 7Z to ZIP on this site. The file stays in your browser and is not uploaded. The limit is 100 MB. Keep the original until the download has been opened in the program that will use it. Do the test with a short or simple file first when the real file is large. A one-page PDF, a single photo, or a one-minute clip will show you whether the output is the kind of file you needed. After that test looks right, run the real file once. Keep both the ZIP original and the 7Z download until the receiving person or the upload form accepts it. Open the archive ZIP to 7Z gives you before you delete the one you started with. Password-protected files fail. Some Unix downloads hide a TAR inside gzip or bzip2, so one conversion may not be the last step. ZIP is the file you can hand to a phone or a Windows PC without an extra app. Creating RAR or 7Z still needs a desktop program.
Here is the decision for ZIP to 7Z. You start with ZIP and you stop when a real program accepts 7Z. RAR, 7Z, TAR, gzip, and bzip2 can be unpacked into ZIP here. It cannot create a new 7Z. That is a desktop job. If those two sentences describe a tradeoff you do not want, do not convert. Renaming the extension by hand will not do this job. Running the tool twice on its own output will not do it either.
Use 7-Zip or PeaZip on your computer. If you have a 7Z and need something everyone can open, use 7Z to ZIP on this site.
A related step, if you still need one, is RAR to ZIP.
Other jobs start from the homepage, where each tool is named for the conversion it actually does.