Compress PPTX
Compress a presentation in your browser — and find out first whether it is even worth doing.
Your presentation is opened and rebuilt inside this page. It is never uploaded, which matters when the file is a contract, a set of results or anything else you would not hand to a stranger.
Compression
Turning this off converts transparent images to JPEG, which is smaller but puts a solid box behind anything that was see-through.What this tool does
A .pptx file is a ZIP archive of XML and images, and its size is almost always the images. Choose your file and the breakdown appears first: how much is images, how much is document content, and which parts are largest. If compressing will not help, it says so. If it will, reducing the largest image dimension to 1920 px at about 75% quality is usually the right setting.
Opens the presentation, reports exactly what is taking up the space, and says whether compressing is worth doing.
Recompresses embedded images at a quality and maximum dimension you choose, leaving vector drawings, animated images and anything that would grow untouched.
How to use it
- Choose your .pptx file.
- Read the breakdown. If images are a small share of the size, stop here — there is nothing to recover.
- Set the largest image dimension to 1920 px and quality to about 75.
- Compress, check the saving, and download.
Why use this compressor
Presentations with large images are hard to email. Checking what takes the space, then recompressing images, shrinks them without opening PowerPoint.
Why we built it
We built the PPTX compressor to show where the size actually is before offering to compress, because a .pptx is a ZIP and the weight is usually in a few images. Compress the pictures with the image compressor and compress documents with compress DOCX.
For a neighbouring job there is also the Compress XLSX, the PPTX to Text Converter and the Markdown to DOCX Converter.
Who this tool is for
- People who cannot email a heavy presentation
- Teachers and students submitting slides
- Office staff archiving decks
When to use it
- Meeting an email size limit.
- Reducing a deck for sharing.
- Finding what makes a file large.
- Optimising before upload.
Why a presentation gets large
It is almost never the content.
A .pptx file is not a single document — it is a ZIP archive containing a set of XML files describing the content, plus every image, font and media clip embedded in it. Renaming one to .zip and opening it shows exactly that.
This matters because the two halves behave completely differently. The XML is text, and text deflates extremely well — it is already compressed inside the container, typically to a small fraction of its raw size. Images are already-compressed binary, and the ZIP layer can do almost nothing with them.
So in practice the size of a large presentation is its images, and very little else. That is why this tool shows the breakdown before it offers to compress anything: if the images are five per cent of the file, no amount of compression will help, and it is better to be told that than to run a slider and wonder why nothing happened.
A single photograph straight from a phone can be 5 MB. Ten of them makes a 50 MB presentation whose actual content is a few hundred kilobytes.
What actually reduces the size
Two things, in this order.
Dimensions first. This is almost always the larger win and the one people skip. A modern phone photo is around 4000 by 3000 pixels. Displayed on a slide, in a page margin, or in a cell, it will be shown at perhaps 1200 pixels across. Every pixel beyond what is displayed is carried, stored and emailed for nothing. Reducing the longest edge to 1920 typically removes three quarters of the data before quality is touched at all.
Quality second. JPEG quality is a trade, and between about 70 and 80 the loss is genuinely hard to see on screen. Below 50 it becomes visible on photographs, particularly around sharp edges and on skin.
| Change | Typical effect on image data |
|---|---|
| 4000 px down to 1920 px | Removes roughly three quarters |
| 1920 px down to 1280 px | Removes roughly half of what remains |
| Quality 92 to 80 | Removes roughly a third, invisibly |
| Quality 80 to 60 | Removes roughly another third, visible on photos |
| Below quality 50 | Clearly visible degradation |
What is deliberately left alone
The cases where compressing does damage.
Vector drawings. Diagrams, charts and shapes pasted from other Office applications are often stored as EMF or WMF metafiles — line art, not pictures. They are already compact, they scale to any size without loss, and pushing one through a JPEG encoder turns crisp lines into a blurry raster at whatever resolution it happened to be. This is the single most damaging thing a naive compressor does, so those parts are never touched.
Animated images. Re-encoding a GIF as a still keeps one frame and silently discards the rest.
Small images. Icons and bullets of a few kilobytes cost quality to re-encode and save nothing measurable, so anything under about 20 KB is passed through.
Transparency, unless you turn it off. A logo with a transparent background converted to JPEG comes back with a solid rectangle behind it, which is obvious and hard to undo. Keeping transparency means those images stay PNG and shrink less.
Anything that got bigger. Flat graphics and screenshots sometimes re-encode larger than they started, and some PNGs were compressed by better tools than a browser has. Wherever the new version is not smaller, the original is kept.
Nothing is uploaded
The file is opened, examined and rebuilt entirely inside this page. It is not sent anywhere, which matters for a presentation more than for most things — these are contracts, financial models, patient lists, unpublished work.
A practical consequence beyond privacy: there is no upload wait, no file size cap and no queue. A 200 MB file is processed at the speed of your computer rather than the speed of your connection.
The trade is that everything runs in one browser tab. A very large file with many images will take a noticeable time and some memory while it works.
Presentations in particular
Decks are the worst offenders, for a specific reason: full-bleed background images. A photograph covering an entire slide is displayed at the projection resolution, which is 1920 pixels across on almost every projector and screen in use. A 6000-pixel original carries nine times the data for no visible benefit.
The second common cause is the same image used on many slides. PowerPoint usually stores it once and references it, but images pasted repeatedly rather than copied as a slide element can end up duplicated. If the breakdown shows several parts of identical size, that is what has happened, and replacing them with one image reused is a bigger win than any compression setting.
Note also that PowerPoint keeps the whole of a cropped image. Cropping a photo on a slide hides the edges rather than deleting them, so a heavily cropped 5 MB photo still costs 5 MB. Recompressing helps, but genuinely deleting the cropped area requires PowerPoint's own "Compress Pictures" with "Delete cropped areas of pictures" ticked.
Embedded video is a separate matter. This tool copies audio and video across untouched, so a deck built around a video clip will barely shrink here — the clip needs shortening or linking to instead of embedding.
What you give it, and what you get back
| Item | Details |
|---|---|
| Input | A .pptx file. |
| Options | Image quality and maximum dimension. |
| Output | A smaller .pptx and a report of the saving. |
Issues you may run into
| What you see | Why it happens | What to do |
|---|---|---|
| The file will not open | It is an older format or is password protected. | Save it in the modern format (.docx, .xlsx or .pptx) without a password. |
| Little saving | The file has few images. | The report says if it is worth it. |
| Images look soft | Quality is low. | Raise quality or dimensions. |
Assumptions and limitations
- Only the modern .pptx format. The older .ppt format is a completely different binary format and cannot be opened here — save it as .pptx in PowerPoint first.
- Password-protected files cannot be opened, since an encrypted file is not a readable ZIP.
- Audio and video are copied across untouched. This tool does not re-encode them, so a file dominated by video will barely shrink.
- Vector drawings, animated images and small images are deliberately left alone.
- Images are re-encoded using the browser's own encoders, which are good but not as good as a dedicated image tool.
- Everything happens in one browser tab, so a very large file needs patience and memory.
- Cropped images are re-encoded at their full stored size — Office keeps the whole original behind a crop, and this does not discard the hidden part.
- Duplicate images are not detected or merged. If the same picture appears as several parts, this will recompress each separately rather than combining them.
Frequently asked questions
How do I make a presentation smaller?
Choose the file and look at the breakdown first. If images are most of the size, reduce the largest image dimension to 1920 px and set quality to about 75 — that combination typically removes most of the excess without any visible difference. If images are a small share, there is little to be gained.
Why is my presentation so large?
Almost certainly embedded images at their original camera resolution. A phone photo is around 4000 pixels across and several megabytes; PowerPoint stores it in full even though it is displayed much smaller. The actual content is usually a tiny fraction of the file.
Will compressing lose quality?
Images are re-encoded, so yes, in principle. At quality 70 to 80 the loss is very hard to see on screen. Reducing dimensions is the bigger saving and is usually invisible too, because the images were being displayed far smaller than they were stored. Vector drawings, animated images and small images are not touched at all.
Is my presentation uploaded anywhere?
No. It is opened, examined and rebuilt inside this page on your own device. Nothing is transmitted, which is also why there is no file size limit and no queue.
Why did the file barely get smaller?
Because its size was not images. The XML that holds your content is already deflated inside the container, so there is very little left to recover. The breakdown shown before compressing tells you this in advance, and the result says so plainly rather than pretending otherwise.
Will it still open in PowerPoint?
Yes. The container is rebuilt with the same parts in the same places — only the image data inside it changes. The preview thumbnail is optionally removed, and PowerPoint regenerates that on the next save.
What about the older .ppt format?
It cannot be opened here. The old .ppt format is a binary format from before Office moved to ZIP-and-XML, and nothing about this approach applies to it. Open it in PowerPoint and save as .pptx first — which usually makes it smaller on its own.