How to Resize an Image on Windows, Mac, and Online (Free)

To resize an image, open it in the right tool and enter new pixel dimensions with the aspect ratio locked — Paint on Windows, Preview on Mac, the Photos crop tool on iPhone, or a free online tool like iLoveIMG for anything else. Resizing changes the pixel count (for example 4000×3000 down to 1200×900). It is not the same as compressing, which shrinks the file size in MB without changing the dimensions. If your real goal is a smaller file for email or upload, see how to reduce image file size instead.

Resize vs. compress: the difference that trips everyone up

Resizing down usually shrinks the file too, because fewer pixels means less data. But two images with identical dimensions can have very different file sizes, so decide which problem you actually have before you start.

Method 1: Windows (built-in, no install)

Photos app

1. Open the image in Photos.
2. Click the … (See more) menu in the top toolbar, then choose Resize (on some versions it sits under Edit).
3. Pick a preset size, or choose Define custom dimensions and enter the width and height.
4. Save — Photos writes a resized copy and leaves the original untouched.

Paint

1. Right-click the image → Open with → Paint.
2. Click Resize in the toolbar.
3. Choose Pixels (exact dimensions) or Percentage (e.g. 50%), enter the new value, and leave Maintain aspect ratio ticked.
4. Click OK, then File → Save As → JPEG or PNG to keep a copy.

The aspect-ratio lock is the important part. With Maintain aspect ratio ticked, changing the width recalculates the height automatically. Untick it and the image stretches — faces get wider, circles turn into ovals.

Method 2: Mac (built-in, no install)

Preview

1. Open the image in Preview.
2. Choose Tools → Adjust Size.
3. Type a new Width or Height — the other updates automatically while Scale proportionally is ticked. You can also use Fit into to cap the longest side.
4. Click OK, then File → Save (or File → Export to write a separate copy).

Finder Quick Actions

1. Select the image (or several) in Finder.
2. Right-click → Quick Actions → Convert Image.
3. Choose the format (JPEG, PNG, HEIC) and a size preset such as Small, Medium, Large, or Actual Size.
4. Decide whether to keep metadata, then click Convert.

Quick Actions is the fastest route for batch work and for turning iPhone HEIC files into JPEG (see how to convert HEIC to JPG), but its size presets are coarse. For an exact pixel count, use Preview’s Adjust Size.

Method 3: iPhone and Android

The built-in Photos editors crop to a shape (aspect ratio) rather than to an exact pixel size:

1. Open the photo → tap Edit.
2. Tap the crop/rotate icon.
3. Tap the aspect-ratio button and pick Original, Square, 16:9, 4:5, etc., or drag the corners freehand.
4. Tap Done.

For an exact target like 1080×1080, use a free app — Image Size (iOS) or Photo & Picture Resizer (Android) — where you type the width or height and the app scales the whole image without cutting anything off. Full walkthrough: how to resize an image on iPhone.

Method 4: Free online tools

Online tools work on any device and suit batch resizing or exact dimensions when you can’t install anything:

• iLoveIMG — resize by pixels or percentage, batch upload, no signup.
• Canva — resize inside a design and export at custom dimensions; best when you’re making a post, not just editing a photo.

Upload → set dimensions → download. One caveat: don’t upload confidential images (ID documents, private photos) to a site you don’t know — use a built-in desktop tool instead.

Aspect ratio and avoiding distortion

Aspect ratio is the relationship between width and height (16:9, 4:3, 1:1). Two rules cover almost everything:

• Lock it when you resize. Preserving the ratio is what keeps the image looking normal, and every tool above has a checkbox for it — leave it on.
• Only unlock it deliberately. Stretching is occasionally intentional, but usually it just looks wrong.

If you need a different shape rather than a different size, don’t stretch — crop instead. Cropping cuts off the edges to change the ratio while keeping the subject’s proportions intact.

What size do I need?

Platform specs change often, so treat these as starting points. For print, aim for 300 DPI at the final print size.

Common mistakes

• Confusing resize with compress. Changing dimensions when you only needed a smaller file — or the reverse — wastes time.
• Unlocking the aspect ratio by accident. One careless change stretches the whole image.
• Enlarging a small image. Upscaling adds no real detail; it just interpolates and looks soft.
• Re-saving a JPEG again and again. Each save re-compresses it and adds artifacts. Edit once from the original.
• Overwriting the original. Use Save As or Export so you keep the full-resolution file.

FAQ

What’s the difference between resizing and compressing an image?

Resizing changes the pixel dimensions (width × height); compressing reduces the file size in KB/MB while keeping the dimensions. For file size alone, see how to reduce image file size.

How do I resize an image without losing quality?

Resize downward and keep the aspect ratio locked. Shrinking discards pixels and stays sharp. Enlarging beyond the original resolution always looks softer, because no tool can invent detail that isn’t there.

How do I resize an image to an exact size like 1080 × 1080?

Use Paint on Windows, Preview → Tools → Adjust Size on Mac, or iLoveIMG online, and type the width and height directly. On a phone, use a free app like Image Size.

Can I resize several images at once?

Yes. Select multiple files in Finder → Quick Actions → Convert Image on Mac, use iLoveIMG’s batch mode online, or a dedicated batch tool on Windows.