iOS has no compress button in Photos. There are three real routes: the size picker in Mail, a Shortcut you build once, or a browser tool.
Compose a message, attach the photo, then tap Send. iOS offers Small, Medium, Large or Actual Size, showing the resulting file size beside each. Pick one, send it to yourself, and save the result. It is crude but takes seconds and needs nothing installed.
Open Shortcuts, create a new shortcut, and add the Resize Image action followed by Convert Image, which exposes a quality setting. Set it to accept images from the share sheet. From then on the whole job is Share → your shortcut, and it works on batches.
Open the compressor on this page in Safari, tap the drop zone to pick from your photo library, choose a quality or an exact KB target, and save the result back. It runs on the phone itself, so the photo is never uploaded.
Apple's position is that you should not have to think about file size — iCloud Photos handles storage, and sharing goes through mechanisms that make their own decisions. That works until something demands a file under 100 KB, at which point the Photos app offers you nothing.
This is not a gap you can close with a setting. Either you use a route that happens to expose size, such as Mail, or you build one with Shortcuts, or you use a tool.
By default a modern iPhone saves photographs as HEIC, which stores them at roughly half the size of an equivalent JPEG. It is a genuine improvement and you should generally leave it on.
The problem is everyone else. Windows needs an extension to open HEIC, plenty of web forms reject it outright, and many desktop applications do not recognise it. If you are constantly converting, switch the camera to JPEG: Settings → Camera → Formats → Most Compatible. You will roughly double your photo storage in exchange for files that open everywhere.
Note that iOS often converts HEIC to JPEG automatically when you share — which is why a photo that looks like a HEIC on your phone frequently arrives as a JPEG.
A recent iPhone photograph is around 4000 pixels on its longest edge. For a web upload, an email, or almost any form, that is far more than anyone needs.
Reducing the longest edge to 1600 pixels cuts the file by roughly three quarters before any quality setting is touched, and the result still looks sharp on any phone or laptop screen. Do that first and the quality slider barely has to work.
Menu names and options move between releases. If a step below does not match what you see, the underlying capability is usually still there under a nearby name — and the browser tool on this page works identically on every version.
These run in your browser on any device, so nothing is uploaded and there is nothing to install.
Shrink JPG and JPEG photographs with a quality slider or an exact target size.
Open the toolWhere a photograph stops being a compromise.
Open the toolBy pixels or percentage, aspect ratio locked, across a whole batch.
Open the toolStrip GPS coordinates, camera model and timestamps before you publish.
Open the toolQuestions
Every answer below is present in the page source, expanded, so it can be read without opening anything.
No. Photos has cropping, adjustment and markup, but no compression or resizing option of any kind. Anyone telling you to look for one in that app is describing software that does not exist.
Attach the photo to a Mail message and tap Send — iOS then offers Small, Medium, Large or Actual Size with the file size shown beside each. Send it to yourself and save the attachment. Alternatively, open the compressor on this page in Safari, which needs no installation either and gives you an exact KB target.
It depends on the tool. A great many online compressors upload your file to their server. The one on this page does not — the work is done by Safari on the phone itself, so the photo never leaves the device. You can prove it by turning on Airplane Mode after the page loads.
Reduce the dimensions first — 1000 to 1200 pixels on the longest edge — then compress. At full 4000-pixel resolution, 100 KB gives the encoder about one byte per forty pixels, which no setting can make look good. The exact-size pages on this site do both steps in one pass.
Only if compatibility is a recurring problem for you. HEIC files are about half the size for the same quality, which is a real benefit. If Windows machines and upload forms keep rejecting them, Settings → Camera → Formats → Most Compatible switches to JPEG at the cost of roughly doubling your storage use.
You probably chose Actual Size at the send prompt, or used AirDrop instead, which always sends the untouched original. Check that you are opening the received attachment rather than the original still sitting in your library.
From the blog
More background from the blog.
Attachments are base64-encoded in transit, which inflates them by about a third. A 20 MB limit is really a 15 MB limit. Resize to 1600 pixels on the long edge and encode at quality 80, and a photograph lands near 150 KB.
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A photograph from a phone can carry the coordinates of the place it was taken, the camera serial number and the exact timestamp. Removing that data is straightforward. Removing it carelessly rotates your photos sideways.
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Resize before you compress. Measured on one photograph: half the width at quality 80 produced a 16.4 KB file, while full width at quality 40 produced 20.6 KB and looked far worse. The order of operations matters more than the settings.
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