Why Zipping Photos Doesn't Make Them Smaller

You have forty photos that are too big to email. Zipping seems like the obvious move — it is called a compressed folder, after all. So you zip them, check the result, and the ZIP is 118MB instead of 120MB.

This is not a bug, and you have not done it wrong. Zipping photos almost never saves meaningful space, and understanding why takes about two minutes and saves you from trying it again.

Microsoft says so in its own documentation: zip a collection of JPEGs and the resulting folder will be roughly the same size as the pictures were to begin with.

Both things are looking for the same thing

Compression works by finding patterns and storing them more efficiently. If a file contains the same sequence a thousand times, a compressor can record it once with a note saying "repeat this a thousand times". The more redundancy in the data, the more there is to save.

A text file is full of redundancy — repeated words, repeated spaces, a small alphabet — which is why text often compresses to a fifth of its original size.

A JPEG has already been through exactly this process. When the image was saved, the JPEG encoder found the patterns, exploited them, and threw away detail your eye was unlikely to notice on top of that. What comes out the other side is close to random-looking data with the redundancy already squeezed out.

When ZIP then examines that file, it looks for repetition and finds almost none, because JPEG got there first. There is nothing left to save.

The same is true of PNG, which uses lossless compression internally, and of HEIC, WebP, MP3 and MP4. All of them arrive at the ZIP already compressed.

Why a ZIP can end up slightly larger

A ZIP file is not only the compressed data. It also stores a directory of what is inside, the original filenames, timestamps, folder structure and a checksum for each entry.

That overhead is small, but when the compression saves nothing, the overhead is all that changes. Zip a folder of photos and the result can come out a fraction of a percent bigger than the originals. This surprises people, but it is the expected outcome when you package data that cannot be compressed further.

ZIP is lossless, and that is the point

Here is the conceptual difference that explains everything above.

ZIP is lossless. Every byte you put in comes back out identical when you unzip. That is essential for a document or a spreadsheet, where changing a single byte could corrupt the file. But it also means ZIP can never discard anything, and discarding is where the big savings in images come from.

Image compression is lossy. A JPEG encoder is allowed to throw detail away permanently, because the goal is a picture that looks the same, not a file that is bit-for-bit identical. That freedom is why saving a photo at a lower quality can cut 80 percent of the file size while ZIP cuts none of it.

If you need photos to be genuinely smaller, you need something that is allowed to throw data away. ZIP is not.

When zipping photos is still worth doing

None of this means ZIP is useless here. It is just doing a different job.

Bundling. One attachment instead of forty is easier to send and easier for the recipient to handle. This alone is usually reason enough.

Preserving structure. If your photos are organised into folders, a ZIP keeps that arrangement intact. Attaching files individually flattens everything.

Protecting the files in transit. Some email systems and chat apps re-compress or strip metadata from images they recognise as images. Inside a ZIP they are just data, so they arrive exactly as they left.

Lots of very small files. This one is about disk usage rather than the files themselves. Storage is allocated in fixed-size blocks, so a 2KB icon can occupy a full block and waste the remainder. Pack thousands of tiny files into one archive and that wasted space disappears. It makes no difference for a few dozen photos from a phone.

Formats that are not already compressed. BMP, uncompressed TIFF, RAW camera files and layered PSDs all compress substantially in a ZIP, sometimes by half, because their redundancy is still intact. If your "photos" are actually scans saved as TIFF, zipping genuinely helps.

There is also a niche exception: some archiving tools offer a special lossless JPEG mode that re-packs the image data using a better algorithm than JPEG's own, typically saving 20 to 25 percent. It works, but the recipient needs the same software to open it, which is usually more friction than it is worth.

What to do instead

If the goal is smaller files, work on the images directly.

Resize first. A phone photo is around 4000 pixels wide. Most uses need a fraction of that, and cutting the dimensions cuts file size far more than any quality setting will. Use the resizer on the whole batch at once.

Then compress. Re-encode at a lower quality with the image compressor. Quality 75 is invisible on most photographs and typically removes 60 to 80 percent of the file size.

Convert HEIC first if needed. iPhone photos arrive as HEIC, which many services reject outright. Convert them before anything else.

Then, if you still want one file to send, zip the compressed versions. That is the right order: compress the images with a tool that is allowed to discard data, and use ZIP for the bundling it is actually good at.

The short version

ZIP looks for redundancy. JPEG and PNG have already removed theirs, so there is nothing left for ZIP to find, and the archive's own overhead can make the result marginally larger. ZIP is lossless and therefore cannot throw anything away, which is exactly what shrinking a photo requires. Compress the images first, then zip them for convenience.