What iOS gives you
iOS has no setting that makes a photo a particular number of kilobytes. The closest built-in option is the Preview app's Export, on iOS versions that include Preview:
- Open the Preview app and open the image.
- Tap the menu next to the file name, then Export.
- Choose JPEG and drag the Size slider to the left for a smaller file.
- Save it, choosing where it goes and, if you like, a new name.
The slider trades quality for size but doesn't let you type “50 KB”, so it can take a few tries — and a 12-megapixel photo usually won't get that small at its full width and height without also being made smaller in pixels.
Free, in Safari on your iPhone: our web tool
Compress a photo to 50 KB works in Safari on the iPhone. Choose the photo from your library, and it finds the best quality that fits under 50 KB, shrinking the width and height only if it has to, and shows the final size and dimensions before you download. The photo is processed in your browser and never uploaded. For other limits use compress to any KB, 20 KB or 100 KB; if the form also asks for exact pixel dimensions, resize first.
Checklist for a form
- File type: forms nearly always want JPG/JPEG. The iPhone's default HEIC is often refused — see convert HEIC to JPG.
- Minimum as well as maximum: “20–50 KB” means a 10 KB file is also rejected. Start from the original photo, not one already sent through a messaging app.
- Kilobytes: some sites count 1 KB as 1,000 bytes and others as 1,024. A file under 50,000 bytes passes both.
- Plain background: fine detail costs bytes; a face against a plain wall keeps more quality at 50 KB than one in front of leaves.
Doing it with Oxid Photos
Oxid Photos (not released yet) has the same engine in the app. Choose Compress, pick up to 10 photos from your library (free), choose Under 50 KB — there are also 20 KB, 100 KB, 200 KB, 500 KB and 1 MB — and each result shows its new size and width × height, how it compares in quality, and a plain warning if a photo couldn't get under the limit. Save the results to Photos or share them, for example to Files. Sizes are decimal: 50 KB means 50,000 bytes.
It is free; Pro ($2.99 once) lets you do any number of photos at once and save your own presets. About Oxid Photos.
Sources
The iPhone steps on this page were checked on 13 October 2026 against Apple's own support pages. Menu names can move between iOS versions; if yours differs, Apple's page for your version is the one to follow.
- Export or compress PDFs and images in Preview on iPhone — Apple Support
- Using HEIF or HEVC media on Apple devices — Apple Support