JPG vs JPEG: is there any difference?

The short answer

JPG and JPEG are the same thing. Same format, same compression, same quality, same everything. A file called photo.jpg and a file called photo.jpeg can be byte-for-byte identical, and usually are.

There is no quality difference, no compatibility difference, and no reason to prefer one over the other beyond habit. If someone tells you JPEG is the higher-quality version, they are mistaken.

Why there are two names for one format

The format is named after the group that created it, the Joint Photographic Experts Group, so JPEG is the original and correct spelling.

Early Windows, built on MS-DOS, allowed filenames of only eight characters plus a three-character extension. Four letters would not fit, so on those systems the format became JPG. Mac and Unix systems had no such limit and kept the full spelling.

Windows removed the restriction in 1995. By then both spellings were everywhere, in millions of files and thousands of programs, and neither was going to disappear. Thirty years later we still have both, for a constraint that has not existed since before most of these files were taken.

“Converting” between them

Search for this and you will find plenty of tools offering JPEG to JPG conversion. There is nothing for them to convert.

If you need a .jpg and have a .jpeg, rename the file. That is the whole operation. It is instant, it is completely lossless, and it needs no software.

On Windows, you may need to turn on file extensions first: in File Explorer, open the View menu and tick File name extensions. On a Mac, click the name once, pause, and click again to edit it. Both will ask you to confirm that you meant to change the extension. You did.

When a website accepts one and rejects the other

This is the real reason most people end up asking the question, and it is worth being clear about: the website is wrong.

Upload forms often validate by checking the file extension against a list of allowed ones. Somebody wrote that list, typed .jpg, and did not think to add .jpeg. Your file is fine. Rename it and it will go through.

If renaming does not fix it, the extension was never the problem. The three usual culprits, in order:

The file is too large

The most common cause by far, and often reported with a misleading error message. See resize or compress — and note that if you are fighting a size limit, reducing the dimensions works where lowering quality often cannot.

The dimensions are outside what is allowed

Plenty of forms cap pixel width or height separately from file size, and plenty of them do not say so. Resizing fixes this.

It is not really a JPEG

A file named photo.jpg that is actually a PNG, a HEIC from an iPhone, or a screenshot saved by some app that ignored the extension. Renaming a file never changes what is inside it. This one needs a real conversion, with PNG to JPG being the usual direction.

What actually differs between two JPEGs

The extension tells you nothing useful. These things do:

• Quality setting. The same photo saved at quality 90 and quality 40 are both JPEGs, and one looks considerably worse. This is the difference people are usually sensing when they think the format changed.
• Dimensions. The main driver of file size, far more than the quality setting. Covered in why is my JPEG so big.
• Metadata. One file may carry the camera model, the date and the GPS coordinates where it was taken. The other may have had all of that stripped. Same format, very different things to publish.
• Colour profile. An embedded profile tells software how to interpret the colours. A file that has lost its profile can look washed out, and people often blame the format.

So if two JPEGs look different, the answer is in one of those four, never in whether the name ended with three letters or four.

Frequently asked questions

Is there a difference between JPG and JPEG?

No. They are the same image format, produced by the same encoder, and a file with either extension contains exactly the same kind of data. The only difference is three letters versus four. Nothing about quality, compression, colour or compatibility changes between them.

Why do both JPG and JPEG exist?

The format is named after the Joint Photographic Experts Group, so JPEG is the original spelling. Early versions of Windows, through MS-DOS, only allowed three-letter file extensions, so the name was shortened to JPG on those systems. Windows dropped that limit decades ago, but by then both spellings were in circulation and neither ever went away.

How do I convert a JPEG to a JPG?

You do not need to convert anything, because there is nothing to convert. Renaming the file from photo.jpeg to photo.jpg is a complete and lossless solution, and it does not touch the image data at all. Any tool offering to convert between the two is performing a rename, or worse, re-encoding your image and losing quality for no reason.

Why did a website reject my JPEG but accept a JPG?

Because that site has a badly written upload check that compares file extensions against a list somebody forgot to put .jpeg on. It is a bug on their end, not a problem with your file. Renaming the file fixes it instantly. If renaming does not fix it, the real cause is usually the file size, the pixel dimensions, or a file that is not actually a JPEG despite its name.

Which should I use, .jpg or .jpeg?

Use .jpg. It is more widely used, it is what most cameras and phones produce, and it is the one that badly written upload forms are most likely to accept. There is no technical advantage either way, so pick the one that causes the fewest problems.