How to reduce image file size on any device

How to reduce image file size: the three levers every tool pulls

Every app on every device pulls one of three levers, and they stack: fewer pixels, a lower quality, a newer format. We ran our 9.8 MB camera photo, 4964 × 2782 pixels, through each of them.

Fewer pixels: resize or crop to the size it is shown at

A photo’s bytes follow its pixels. At 1920 pixels wide, the camera photo keeps 15.0% of its pixels and weighs 140.3 KB, 1.4% of its bytes. At 1280 wide it weighs 73.6 KB; at 800 wide, 35.2 KB. Chrome’s Lighthouse puts the rule plainly: a page “should never serve images that are larger than the version that’s rendered on the user’s screen.” The image resizer sets the width in one step.

A crop counts too. Our 1920 × 1280 reference photo, saved as PNG, weighed 994.3 KB at Auto; cut to its 1280 × 1280 centre square, it weighed 705.5 KB. The part you keep holds its full detail, which a resize does not.

A lower quality: how to reduce a JPEG image’s size

At full size, with every pixel kept, the camera photo weighs 2,598.6 KB at quality 95, 807.1 KB at 85, 542.3 KB at 75 and 307.9 KB at 50. The libjpeg guide puts photos between 50 and 95, and warns that above about 95 the file grows “dramatically” for a gain “rarely perceivable by human vision.” To compress JPEG files without guessing, leave the quality on Auto.

To reduce image file size without losing quality you can see, lower the quality until the before-and-after view shows a change, then step back one notch. The eye is the test, not the number: the same setting looks different on a sky and on a page of text.

A newer format: HEIC, WebP and AVIF

The makers’ own claims are big. Google says lossy WebP is 25 to 34% smaller than a comparable JPEG at the same SSIM score. The Alliance for Open Media says AVIF saves “over 50%” against JPEG and “over 30%” against WebP. Apple says HEIF uses less storage “while preserving the same visual quality.”

On our camera photo at full size, the AVIF claim holds: 288.0 KB against 605.5 KB for the JPEG at Auto, 52% smaller, with WebP at 329.0 KB, 46% smaller. On our 1920 × 1280 reference photo the AVIF claim holds too: 123.9 KB against 273.9 KB for the JPEG, 55% smaller. WebP is less even: 218.9 KB, only 20% smaller, short of Google’s figure. Two reasons, both on record. The JPEG standard says compression depends on “the characteristics of the particular image”. And Auto sets each format’s quality by eye on a test set, not at the equal SSIM Google measured at. The whole comparison is in AVIF vs WebP vs JPG.

The catch is where the file goes. The Alliance for Open Media dates AVIF support on phones to Android 12 and iOS 16. Email, upload forms and older software still expect a JPEG.

Which lever to pull first

1. Pixels. Resize to the size the image is shown at, or the size a form asks for.
2. Quality. Leave it on Auto, or lower it until you see a change and step back.
3. Format. A newer one when the place it goes can open it.
4. A cap last. When a form names a number in KB, set it as the maximum.

How to reduce image file size on iPhone

For a photo you already took, Preview on iOS 26 and later is the built-in app Apple documents for exact pixels and a smaller file; on any iPhone, a browser compressor in Safari does both. For the photos you take next, choose High Efficiency and 12 MP in Settings, Camera, Formats. The guide on how to resize an image on iPhone walks through every route.

Photos you already took: Preview, a crop or the browser

In Preview, More, Adjust Size gives the photo fewer pixels, and Export has a Size slider for HEIC and JPEG: left for a smaller file. A shortcut can resize too, though Apple’s Shortcuts guide does not document the action’s options.

Photos itself has no resize box; a crop there removes pixels. A real iPhone 12 Pro HEIC of 1,956.0 KB, resized by our engine to 1080 × 1920, came to a 276.5 KB JPEG or a 151.1 KB AVIF.

Photos you take next: Formats and Photo Mode

High Efficiency saves HEIF, which Apple says takes less storage at the same visual quality. On supported models, Settings, Camera, Formats, Photo Mode switches the main camera from 24 MP to 12 MP: half the pixels in every photo. Resolution Control and ProRAW are what make the 48 MP files, so leave them off unless you need them. Most Compatible saves JPEG, which opens everywhere at more bytes a photo; how to convert HEIC to JPG covers that trade.

Sending: Messages and Mail

Apple says your iPhone “can compress photo and video attachments when necessary.” To send smaller photos on purpose, open Settings, Apps, Messages and turn on Send Low Quality Photo Previews. In Mail, a file over your email account’s limit goes by Mail Drop instead.

How to reduce image file size on Android

On a Samsung Galaxy, the Gallery app resizes a photo by a percentage. On any Android phone, a browser compressor in Chrome does the same with a KB cap. For the photos you take next, choose HEIF and 12 MP where the camera offers them.

Samsung Galaxy: Gallery, Edit, Resize

1. 1

   Open the photo in Gallery and tap Edit

   Samsung built the resize into the Gallery’s photo editor.

2. 2

   Tap More options, then Resize

   Pick a percentage. Samsung does not offer sizes larger than the original.

3. 3

   Tap Done, then Save copy

   Save copy keeps the original. The smaller size shows in the image details.

What a percentage does, measured: at 50%, our camera photo became 2482 × 1391 and 209.6 KB as a JPEG at Auto; at 25%, 1241 × 696 and 70.5 KB.

Any Android phone: the camera’s resolution and HEIF

Samsung’s camera saves HEIF under Photo format, which Samsung says saves space, and keeps Resolution in the Quick controls. On the Galaxy S26, Photo enhancer on Balanced or Prioritize speed saves 12 MP photos; only Prioritize quality saves 24 MP. Pixel phones shoot 50 MP only on Pro models, and only after you set Resolution to 50 MP in the Pro tab.

Google Photos Storage saver shrinks the backup, not the photo you send

Storage saver compresses the backed-up copies and resizes anything over 16 MP to 16 MP; Express resizes to 3 MP. Both are backup settings. Neither hands you a smaller file to attach, so resize or compress a copy for that.

How to make an image’s file size smaller on a Mac

In Preview, resize with Resample image ticked, then export as JPEG at a lower quality or as HEIC. For a Photos library, export at a smaller size. The guide on how to resize an image on Mac covers the main built-in routes and measures Terminal’s sips against Blinkimg.

Preview: Adjust Size with Resample image, then Export

1. 1

   Choose Tools, then Adjust Size

   Several images open in one window can be resized together: select them in the sidebar first.

2. 2

   Tick Resample image and enter a smaller width

   Preview shows the Resulting Size at the bottom of the dialog before you apply it.

3. 3

   Choose File, then Export

   Pick JPEG and move the Quality slider left, or pick HEIC.

What Apple says Resample image does

Untick Resample image and Preview makes the dimensions smaller “without losing any detail”, in Apple’s words. Apple’s steps to reduce the file size tick it. Check the saved size in the Finder before you send it.

The Finder’s Convert Image

The Finder’s Convert Image converts the selected image to another format or a smaller size. For many files, use sips in Terminal.

A Photos library: File, Export

Photos never shrinks the original in the library; a smaller file is an exported copy. Choose File, Export, set Photo Kind to JPEG, then choose a smaller Size and a lower JPEG Quality.

How to shrink an image’s file size on Windows

In Paint, resize and save as JPEG. Photos has a Resize tool too. For a folder, Microsoft’s PowerToys adds a resize to the right-click menu. For a picture inside Word or PowerPoint, Compress Pictures.

Paint: Resize, then save as JPEG

Choose Resize on the Home tab and set a percentage or pixels, then save as JPEG. Not PNG: our reference photo, a 576.8 KB JPEG, weighed 2,866.3 KB saved as a lossless PNG.

Photos: Resize image

Microsoft names a Resize tool in Photos; these steps are How-To Geek’s, from its Windows 11 guide of December 2024. Open the picture, click the three dots at the top, choose Resize Image, set the pixels, optionally lower the quality, then save.

A folder at once: PowerToys Image Resizer

After installing Microsoft’s free PowerToys, right-click the selected files in File Explorer and choose Resize with Image Resizer. Pick Fill, Fit or Stretch, in centimetres, inches, percent or pixels.

A picture inside Word or PowerPoint: Compress Pictures

Select the picture, open the Picture Format tab and choose Compress Pictures, then a resolution: Print, Web or E-mail. Microsoft notes the change is kept only once you save the file.

How to decrease image file size online, on any device

Open a browser compressor on any device, phone included. Drop up to 50 files, keep Auto or type a Max file size, and download the copies, one ZIP for a batch. Auto took our 1920 × 1280 reference photo from a 576.8 KB JPEG to 273.9 KB, 52.5% smaller. We keep nothing: the files are deleted within 24 hours of the upload.

How to make a photo small enough for email or an upload form

Work back from the limit. Gmail takes 25 MB a message on a personal account. Classic Outlook takes 20 MB for Outlook.com or Gmail accounts, 10 MB for business Exchange by default, and can resize large images for you under File, Info. Mail on a Mac inserts images at their actual size, with smaller sizes in a menu on the message header. To send a whole batch, we put 20 images through one email to show how to compress photos for email.

A form names a KB cap, and pixels are the cheap way under it. On the camera photo, a 100 KB cap alone kept all 4964 × 2782 pixels at 97.3 KB, which cost quality: our quality-10 file weighs 80.8 KB and our quality-30 file 194.8 KB. Resized to 800 wide first, the same photo weighs 35.2 KB at Auto, under the cap with no quality given up. Resize to the pixels the form states, then set the cap. To reduce image size in KB to any number, type it as the maximum; for a portal that still refuses, the checks behind a photo not uploading in an online form are the next stop.

What does not reduce image file size

• Changing the DPI number alone. DPI tells a printer how large to print the same pixels, so the bytes stay.
• Saving a photo as PNG. Our reference photo, a 576.8 KB JPEG, became 994.3 KB as a PNG at Auto and 2,866.3 KB lossless.
• Enlarging. The same JPEG doubled to 3840 × 2560 weighed 712.0 KB.
• Saving again at the same quality. At quality 75 it weighed 253.3 KB after one save and 251.9 KB after ten. The libjpeg guide warns that the loss adds up over repeated cycles, so compress from the original once.
• Zipping a JPEG. The 9.8 MB camera photo went from 9,804.3 KB to 9,796.6 KB in a ZIP’s compression, 0.08% smaller.
• Renaming .heic to .jpg. The name changes; the bytes, and the format inside, do not.

The next step is one photo: drop it into the compressor, keep Auto, and read the size it prints beside the result. When a form names a number, set Max file size to it.