When JPEG to JPG turns JPEG into JPG
Windows, email, and most government forms expect .jpg. A camera or Mac that saved .jpeg is the same kind of photo with the other ending.
What JPEG to JPG changes in the picture
The browser draws the picture and writes a .jpg file. Transparency is flattened to a solid background because JPEG has none.
Do not run this back and forth. The second save is softer than the first. One pass from the original is the right habit.
When JPEG to JPG is the right page
JPEG to JPG sits on this site because JPEG and JPG are not interchangeable, even when they look similar in a file list. Windows, email, and most government forms expect .jpg. A camera or Mac that saved .jpeg is the same kind of photo with the other ending. A few old upload forms demand the letters JPEG or the letters JPG and reject the other. Portals, printers, and chat apps that reject HEIC, WEBP, or AVIF are asking for JPG.
The browser draws the picture and writes a .jpg file. Transparency is flattened to a solid background because JPEG has none.
What you give up by leaving JPEG
JPEG and JPG are the same picture format. Only the file extension differs. This is still a new JPEG save, not a rename of the same bytes, so fine detail softens slightly.
Keep the original photo. The extension change is only for the form.
What you gain, and do not gain, with JPG
The download has to be JPG, because that is the format the next step named. Portals, printers, and chat apps that reject HEIC, WEBP, or AVIF are asking for JPG. It is small and universal for photographs.
Convert once from the best original. A second lossy save only throws away more.
A test that matches the real file
Start from the question the other software asked. If it asked for JPG, JPEG to JPG is the matching page. If it asked for something else, switch tools instead of hoping a similar extension will pass. Windows, email, and most government forms expect .jpg. A camera or Mac that saved .jpeg is the same kind of photo with the other ending. The browser draws the picture and writes a .jpg file. Transparency is flattened to a solid background because JPEG has none. The limit is the part people skip, and it is the part that decides whether the download is usable. Do not run this back and forth. The second save is softer than the first. One pass from the original is the right habit. 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. Check three things in the download: it opens, the JPEG material you cared about is still there, and the file size or the layout is what the form described. A new extension alone is not those three things. If a portal, a teacher, or a client rejects the file, send them the original JPEG as well when you are allowed to. JPEG to JPG is a convenience copy. It is not a new master. Photos fail uploads for three separate reasons: the format name, the pixel size, and the kilobyte size. JPEG to JPG only does the JPEG to JPG step. If the form also prints a pixel size or a 20 KB or 50 KB cap, do that step with the matching tool, starting from the original each time. A second lossy save will not recover detail.
Here is the decision for JPEG to JPG. You start with JPEG and you stop when a real program accepts JPG. Changing the extension family satisfies a form that only checks the name. JPG is lossy. Saving it again softens fine detail. It cannot store transparency. 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.
Do not run this back and forth. The second save is softer than the first. One pass from the original is the right habit.
A related step, if you still need one, is JPG to JPEG.
Other jobs start from the homepage, where each tool is named for the conversion it actually does.