How to reduce image file size without losing quality

The three things that decide an image's file size

Every method of making an image smaller works through one or more of three levers. The first is the pixel dimensions: how many pixels wide and tall the image is. A 12-megapixel phone photo is about 4000 × 3000 pixels. Halving both sides to 2000 × 1500 leaves a quarter of the pixels, and the file shrinks roughly in proportion. This is by far the strongest lever, and for most uses it costs nothing you can see, because screens, emails and web pages rarely show an image anywhere near 4000 pixels wide.

The second lever is the file format. The same picture can take very different amounts of space as JPG, PNG or WebP, depending on what it shows. The third is the quality setting of lossy formats such as JPG and WebP, usually a number from 0 to 100. Lower numbers throw away more fine detail. The relationship is not linear: going from 100 to 85 often halves the file with no visible change, while going from 60 to 40 saves less and starts to show blocky patches and smudges around edges.

Metadata plays a small part too. Photos carry EXIF data such as the date, camera model and often the GPS position, and sometimes an embedded preview. Removing it saves a little space and is good for privacy, but on its own it will not turn a 5 MB photo into a 500 KB one.

Which format to use for which picture

JPG is made for photographs and other images with smooth gradients and lots of detail. It opens everywhere, from old email programs to government upload forms. It cannot store transparency, and at lower quality settings it adds faint halos around sharp edges, which is why text in a JPG screenshot can look fuzzy.

PNG is lossless and is the right choice for screenshots of text, diagrams, logos, charts and anything with flat colours or transparency. For such images it is often smaller than a JPG of the same quality. For photographs it is the wrong choice: a photo saved as PNG is typically several times larger than the same photo as a good JPG. If you have a photo or a screenshot of a photo saved as PNG, converting it to JPG is often the single biggest saving.

WebP can be lossy like JPG or lossless like PNG, and supports transparency in both modes. Lossy WebP is usually noticeably smaller than a JPG of similar visual quality. All current browsers display WebP, so it is a good choice for websites, but some older programs, print shops and upload forms do not accept it. When in doubt, send JPG.

What "without losing quality" really means

Strictly lossless reduction means the decoded pixels are exactly the same as before. That is possible: you can strip metadata, recompress a PNG with a better encoder, or rewrite a JPG's internal tables with a tool such as jpegtran. The savings are real but usually modest, often a few percent and sometimes more for badly saved PNGs. Saving a JPG again, even at quality 100, is not lossless; each lossy save decodes the image and throws away a little more detail.

In everyday use, "without losing quality" therefore means without visible loss at the size the image will be seen. A 1600-pixel-wide photo at 80 % JPG quality looks the same on a laptop screen as the 4000-pixel original, but it is a fraction of the size. Keep the originals for printing, cropping and editing, and always make smaller copies from the original rather than from a copy that has already been compressed.

Reduce image size on Windows with Photos or Paint

The Photos app in Windows 11 has a resize option in the menu behind the three dots, or in the editor, depending on the version. It offers preset sizes and a custom size in pixels, keeps the aspect ratio by default, and in recent versions shows a quality slider for JPG output. It then saves a resized copy, leaving the original untouched. The menus have changed with several Photos updates, so the option may be in a slightly different place on your PC.

Paint is available on every Windows PC and is predictable. Use Resize on the Home tab, or press Ctrl+W, and choose Pixels with Maintain aspect ratio ticked. Then save the copy with File > Save as and pick JPEG picture for photos or PNG picture for screenshots. Paint does not let you choose the JPG quality, so its JPG files are not always as small as they could be.

1. Open the image in Paint and press Ctrl+W.
2. Choose Pixels, keep Maintain aspect ratio ticked and enter a new width, such as 1600.
3. Choose File > Save as, pick JPEG picture or PNG picture and save under a new name.

Reduce image size on a Mac with Preview

Preview has both levers built in. Tools > Adjust Size changes the pixel dimensions; keep Scale proportionally and Resample image ticked, and the dialog shows the resulting size before you apply it. File > Export then lets you choose the format and, for JPEG, a quality slider between Least and Best. Preview shows an estimate of the file size as you move the slider, which makes it easy to aim for an upload limit. To process several images at once, open them together, select all thumbnails in the sidebar and use Adjust Size on all of them.

1. Open the image in Preview and choose Tools > Adjust Size.
2. Keep Scale proportionally ticked, enter a width in pixels and click OK.
3. Choose File > Export, pick JPEG, move the quality slider and watch the estimated file size, then save.

Reduce image size on the command line with ImageMagick

ImageMagick is a free command-line image tool for Windows, macOS and Linux. In version 7 the command is magick; older installations use convert instead. The resize value 1600x sets the width and calculates the height from the aspect ratio, and adding a > sign (in quotes, because the shell treats it as a redirect) only shrinks images that are larger. The strip option removes metadata.

The mogrify command processes many files at once but overwrites them unless you give it an output folder with the path option, so test on copies first. For lossless clean-up of files you have already sized, tools such as jpegtran for JPG and oxipng or optipng for PNG rewrite the files without changing a pixel.

# Resize to 1600 px wide and save as JPG at quality 80
magick in.jpg -resize 1600x -quality 80 out.jpg

# Only shrink images wider than 1600 px, and remove metadata
magick in.jpg -resize "1600x>" -strip -quality 80 out.jpg

# A whole folder, written to the folder "small" (create it first)
magick mogrify -path small -resize "1600x>" -quality 80 *.jpg

Fit an email or upload form size limit

Email services commonly limit attachments to around 20 to 25 MB per message, and attachments grow by about a third when they are sent, because they are encoded as text. Eight photos of 3 MB each add up to 24 MB on disk but to about 32 MB once encoded, which is over a 25 MB limit. Resizing them to 1600 or 2000 pixels wide usually brings each one well under 1 MB.

Upload forms for job applications, visa photos or insurance claims often have much smaller limits, such as 1 MB, 500 KB or even 100 KB, and sometimes exact pixel sizes as well. Start by cropping away what is not needed and setting the pixel size the form asks for, then lower the quality step by step until the file fits. If the form asks for a specific format, use it, even when another one would be smaller.

Reduce image size in your browser with FileReshape

FileReshape's Compress Images tool accepts JPG, PNG and WebP images and saves them again as JPG or WebP. You choose a quality of 90, 80, 70 or 60 %, with 80 % recommended, and optionally a maximum width between 800 and 3840 pixels; wider images are scaled down and narrower ones are left as they are. The list shows the size before and after for every file. If an image would come out larger than it was, because it was already well compressed, you get the original back unchanged. There is no option to aim for an exact file size; lower the quality or the maximum width and check the new size in the list.

Re-encoded images keep only the pixels. Photos are turned upright first, then the GPS position, date taken and camera details are left out, and colours are saved in sRGB. With JPG output, transparent areas become white, so choose WebP to keep them. WebP output works in Chrome, Edge and Firefox; Safari cannot create WebP files. Several images are downloaded together as a zip.

When you need an exact size instead, the Resize Image tool takes a width, a height or both in pixels, or a percentage, keeps the aspect ratio unless you switch that off, and fits the image inside the box when you give both. JPG stays JPG at 92 % quality and PNG stays lossless PNG. The Crop Image tool removes unneeded parts of a picture, PNG to JPG turns photo-like PNG screenshots into much smaller files, and JPG to WebP converts photos for websites. All of these run in your browser, and the images are not uploaded.

1. Open Compress Images and drop your JPG, PNG or WebP images in the box.
2. Choose JPG or WebP, a quality, and a maximum width such as 1920 or 1600 pixels.
3. Click Compress images, check the sizes before and after, and download the image or the zip.