What is available depends heavily on who made your phone. Samsung's Gallery can resize; Google Photos cannot. A browser tool works the same on every device.
Open the photo in Gallery, tap the three-dot menu and look for Resize. Choose a percentage or a pixel size and save. Several other manufacturers have a similar option in their own gallery app — it is worth checking the menu before assuming it is missing.
Open the compressor on this page in Chrome, tap the drop zone to pick photos from your gallery, set a quality or an exact KB target, and save the results. It runs on the phone, so nothing is uploaded, and it behaves identically regardless of manufacturer.
In the Camera app's settings, drop the photo resolution from the maximum to something more modest — 12 megapixels is plenty for anything short of large prints. Every photo you take afterwards is a fraction of the size, and you stop having to fix them one at a time.
Google Photos offers a backup quality setting — previously "High quality", now "Storage saver" — which compresses your photographs to save space in your Google account.
It applies to the cloud copy. The file on your phone is untouched, and downloading it back gives you the original size. If you are trying to satisfy an upload form, this setting will not help you, and a great many guides get this wrong.
Android is a base that manufacturers layer their own software over. Samsung's One UI ships a Gallery app with genuine editing and resizing; other manufacturers ship something more limited; and a device using Google Photos as its only gallery has no resize function at all.
This is why platform guides for Android are so often wrong for the phone in front of you. The two routes that always work are the camera resolution setting and a browser-based tool — neither depends on who made the device.
Modern Android phones often shoot at 50 megapixels or more, sometimes producing files above 15 MB. That is enormous for any ordinary purpose.
Capping the longest edge at 1600 pixels removes the great majority of the data before any quality setting is involved, and the result still looks sharp on any screen. If you never print, consider simply lowering the camera resolution and skipping this step permanently.
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 toolThe classic job portal and admissions form budget.
Open the toolBy pixels or percentage, aspect ratio locked, across a whole batch.
Open the toolOne setting across a whole folder, processed in parallel, downloaded as a ZIP.
Open the toolQuestions
Every answer below is present in the page source, expanded, so it can be read without opening anything.
Not the file on your phone. Its Storage saver setting compresses the copy uploaded to your Google account, leaving the local file untouched. For a smaller file on the device you need your manufacturer's gallery app, a browser tool, or a dedicated app.
There is no guaranteed one, because it depends on the manufacturer's software. Samsung Gallery has a Resize option; many other gallery apps do not. The camera resolution setting and a browser tool are the two routes that work on every Android device.
Open the compressor on this page in Chrome and pick the photo from your gallery. There is nothing to install, no account, and the processing happens on the phone — the photo is not uploaded anywhere.
High-resolution sensors. A 50-megapixel photograph contains four times the data of a 12-megapixel one, and for viewing on screens or sharing you will never see the difference. Lowering the camera resolution is the single most effective fix, and it is permanent.
Essentially no. JPEG and HEIC files are already compressed, so a ZIP archive of them saves a per cent or two at best while making the result harder to open on a phone. Compress the images themselves instead.
Some, by definition, since JPEG is a lossy format. At quality 80 the loss is invisible at normal viewing size. What matters far more is resizing: reducing dimensions to what will actually be displayed is where nearly all the saving comes from, and it costs nothing visible.
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.
9 min read
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.
8 min read
Quality 80 is not 80% of anything. It is an index into a quantisation table. Measured on one photograph: dropping from 100 to 90 removes 77% of the file and 4.2 dB of fidelity; dropping from 40 to 30 removes 17% and costs almost as much.
8 min read