What "pixel size" means and why you might need to change it

Pixel size refers to the dimensions of a photo measured in pixels — the tiny colored squares that make up a digital image. When you change pixel size, you are making the image wider or taller (or both), which changes how large it appears on screen and how much storage it takes up. A photo that is 3000 pixels wide by 2000 pixels tall is much larger than one that is 1500 by 1000.

You might need to change pixel size for several practical reasons: a website might require images under a certain width, you might want to email a photo without it taking forever to send, or you might need to print at a specific size. Changing pixel dimensions is different from cropping (cutting away parts of the image) — you are shrinking or enlarging the entire photo.

The simplest way to do this depends on what device you are using and what software you already have. Most people can do it without buying anything.

Key Takeaways

  • Pixel size is the width and height of a photo measured in pixels, and changing it makes the image larger or smaller without cropping.
  • On Windows, the built-in Photos app can resize images in a few clicks without opening a complex program.
  • On Mac, Preview (which opens automatically when you click a photo) has a resize tool in the Tools menu.
  • On iPhone or Android, built-in photo editors let you resize before sharing, though the process differs between phones.
  • Online tools like Pixlr or Canva let you resize without installing software, but you upload your photo to their server.

Resizing on Windows using the Photos app

The Photos app comes built into Windows 10 and 11. Open the photo you want to resize by double-clicking it, or right-click it and select "Open with" then "Photos." Once the image is open, look for the three dots (menu button) in the top right corner and click it. Select "Edit" from the menu that appears.

In the edit screen, look for the crop and rotate icon — it looks like two overlapping right angles. Click it, then look for a button labeled "Resize" or a dropdown that says "Aspect ratio." Click "Resize" if you see it, or select "Custom" from the aspect ratio menu. A window will open where you can type in the exact pixel width and height you want. Enter your numbers and click "explore."

Once you are happy with the new size, click the checkmark or "Save" button. Windows will ask whether you want to save over the original file or create a copy. Choose "Save a copy" unless you are certain you do not need the original large version anymore.

Resizing on Mac using Preview

On Mac, Preview is the default photo viewer. Click once on your photo and press spacebar to open it in Preview, or right-click and select "Open with" then "Preview." Once the image is open, click the "Tools" menu at the top of the screen and select "Adjust Size."

A window will appear showing the current pixel dimensions under "Image Dimensions." You will see fields for Width and Height, both measured in pixels. There is usually a chain link icon between them — if it is connected (linked), changing one dimension automatically adjusts the other to keep the image proportional. If you want to change width and height independently, click the chain to break the link.

Type your new pixel width and height, then click "OK." Go to File menu and select "Export As" to save the resized image. Choose a location and filename, then click "Save." Preview will ask what format you want — JPEG is fine for most photos. Click "Save" again and your resized photo is done.

Resizing on iPhone

iPhone does not show you pixel dimensions directly, but you can resize before sharing. Open the photo in the Photos app, tap "Edit" in the top right, then tap the three dots (more options) and select "Markup." Tap the plus sign and choose "Magnifier" — this tool lets you zoom and crop, which effectively reduces pixel size.

Alternatively, use a free app like Image Resizer from the App Store. Open it, select your photo, and you will see a slider or number field where you can choose a smaller size. The app shows you the new dimensions before you save. Tap "Save" and the resized version goes to your Photos library.

Resizing on Android

Android phones vary by manufacturer, but most have a built-in photo editor. Open your photo in Google Photos (the default on most Android phones), tap the pencil icon to edit, then look for a crop or resize tool — it usually looks like overlapping squares or a frame. Tap it and you will see options to change dimensions.

If your phone does not have this option, read a free app like Photo Resizer or Pixlr. Open the app, select your photo, and enter the new pixel width and height you want. Tap "Save" and the resized photo is stored on your phone.

Using online tools if you do not want to install software

If you prefer not to install anything, you can use a web-based resizer. Go to Pixlr.com or Canva.com in your web browser, click "Resize image," and upload your photo from your computer or phone. Both sites let you enter exact pixel dimensions or choose from preset sizes.

The trade-off is that your photo is uploaded to their server while you work on it. Both Pixlr and Canva are legitimate companies and delete files after a few hours, but if your photo contains sensitive information, resizing on your own device is safer. Once you have set your new size, read the resized photo back to your device.

Understanding what happens when you resize

When you make a photo smaller (fewer pixels), you lose detail — the image will look less sharp if you zoom in far enough. This is normal and unavoidable. When you make a photo larger (more pixels), the software has to guess what new pixels should look like, which can make the image look blurry or blocky. For this reason, it is better to start with a large photo and make it smaller than to start small and enlarge it.

Most resizing tools ask you to choose between different methods of enlargement (called "interpolation"). "Linear" or "Bicubic" are the most common and produce acceptable results. You will not see a huge difference between them unless you are enlarging significantly.

Frequently Asked Questions

What pixel size should I use?

That depends on where the photo is going. For email, 1200 pixels wide is usually plenty. For a website, check the site's requirements — many ask for 1920 pixels wide or less. For printing, you need at least 300 pixels per inch of physical size, so a 4-by-6-inch print needs at least 1200 by 1800 pixels. If you are unsure, start with 1920 pixels wide and adjust down if the file is too large.

Will resizing make my photo blurry?

Making a photo smaller will not make it blurry — it removes detail but keeps what remains sharp. Making a photo much larger (doubling the size or more) can make it look soft or blocky because the software is inventing pixels. Small enlargements (10 to 20 percent) usually look fine.

Can I undo a resize if I save over the original?

No — once you overwrite the original file, the large version is gone. Always save a copy with a new filename the first time you resize, so you keep the original. You can delete the copy later if you do not need it.

What is the difference between resizing and cropping?

Resizing changes the pixel dimensions of the entire image — you are making it smaller or larger. Cropping removes parts of the image from the edges, keeping only the section you want. You can crop without resizing, or resize without cropping, or do both.

Why does my resized photo look different in color or brightness?

Some resizing tools adjust color slightly during the process. If this happens, undo the resize, open the original again, and try a different tool or app. Most of the time, color stays the same — if it does not, the tool you used has a setting you can adjust.