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

Pixel size is the width and height of a photo measured in pixels — the tiny dots that make up a digital image. When you change pixel size, you are making the image larger or smaller. A photo that is 1920 × 1080 pixels is wider and taller than one that is 800 × 600 pixels.

You might need to change pixel size because a website requires a specific dimension, because you want to email a photo without it taking up too much space, or because you are printing and need to match a certain size. The method you use depends on what device you have and what software is already on it.

Key Takeaways

  • Windows comes with Photos app built in; Mac comes with Preview — both can resize without installing anything new.
  • Resizing to a smaller pixel size makes the file smaller and faster to email or upload, but you cannot enlarge a photo without losing sharpness.
  • Keep the same proportions (aspect ratio) unless you have a reason not to, or your photo will look stretched or squished.
  • Free online tools like Pixlr and Canva let you resize without installing software, though you must upload your photo to their servers.

Resizing on Windows using the built-in Photos app

Windows 10 and Windows 11 include a Photos app that can resize without any extra software. Open the photo you want to resize, then look for a menu icon (three dots) in the top right corner and select "Edit." Tap the crop icon, and you will see options at the bottom of the screen.

Look for "Aspect ratio" or a resize option. Some versions of Photos let you type exact pixel dimensions; others only let you choose preset sizes like "16:9" or "4:3." If you need exact pixel dimensions and the Photos app does not offer that, use Paint instead — it is also built into Windows and gives you full control over width and height in pixels.

To use Paint, right-click the photo file, select "Open with," and choose Paint. Go to Image menu, then "Resize," and you can enter exact pixel width and height. Make sure "Maintain aspect ratio" is checked unless you want to stretch the image intentionally.

Resizing on Mac using Preview

Mac's Preview app handles resizing without installing anything. Open your photo in Preview (double-click it, or right-click and select "Open with Preview"). Go to the Tools menu at the top, then select "Adjust Size."

A window will appear showing the current width and height in pixels. Type in the new width or height you want — if the chain link icon next to the dimensions is connected, the other dimension will adjust automatically to keep the photo from looking stretched. Click OK and then save the file with File > Export to keep the resized version.

Resizing on iPhone or Android

Phone photo apps vary, but most let you crop and resize. On iPhone, open the photo in the Photos app, tap "Edit," then tap the crop icon. You can drag the corners to change size, but this crops rather than truly resizes — it removes parts of the photo instead of shrinking the whole thing.

For actual pixel resizing on a phone, use a free app like Pixlr (available on both iPhone and Android) or Snapseed. Open your photo in the app, look for a "Resize" or "Scale" option, and enter the new pixel dimensions you need. Save the result back to your phone's photo library.

Using free online tools if you do not want to install software

Pixlr.com and Canva.com both let you resize photos in a web browser without downloading anything. Go to the website, upload your photo, and look for a resize or scale option. Type in the pixel width and height you need, and download the result.

The trade-off is that your photo is temporarily stored on their servers while you work. If your photo contains private information or you prefer not to upload to the internet, use the built-in tools on your device instead. Online tools are fastest if you resize photos often and do not want to learn new software.

Understanding what happens when you make a photo smaller versus larger

Making a photo smaller (fewer pixels) always works well — the file gets smaller, it loads faster, and it looks fine. Making a photo larger (more pixels) is the problem. When you enlarge a photo, the software has to guess what the new pixels should look like, and the result is blurry or blocky.

If you have a 640 × 480 pixel photo and you enlarge it to 1920 × 1440, it will look noticeably worse. Start with the largest photo you have if you know you might need to resize it later. If you only have a small photo and need it larger, accept that it will not be as sharp, or look for a higher-resolution version of the original.

Keeping the right proportions so your photo does not look stretched

Every photo has an aspect ratio — the relationship between width and height. A photo that is 1920 × 1080 has a 16:9 ratio (widescreen). A photo that is 1000 × 1000 has a 1:1 ratio (square).

When you resize, most tools have a "lock" or "chain" icon that keeps the aspect ratio the same. If you unlock it and change width and height separately, your photo will stretch horizontally or vertically and look wrong. Leave the lock on unless you specifically want to change the shape of your photo.

Frequently Asked Questions

What is the difference between resizing and cropping?

Resizing shrinks or enlarges the entire photo to new pixel dimensions. Cropping removes the edges and keeps only the center part. If you resize a 1920 × 1080 photo to 960 × 540, the whole image gets smaller. If you crop it, you remove pixels from the sides or top and bottom.

Can I make a small photo larger without it looking blurry?

Not really. Enlarging a photo means adding pixels that did not exist in the original, and the software cannot recreate detail that was never there. If you need a larger size, start with the highest-resolution version of the photo you can find.

What pixel size should I use for uploading to social media?

This varies by platform. Facebook recommends 1200 × 628 for a cover photo, Instagram works best with square photos around 1080 × 1080, and Twitter prefers 1024 × 512. Check the platform's help section for the exact size, then resize your photo to match.

Does resizing a photo make the file smaller?

Yes, if you reduce the pixel dimensions. A 1920 × 1080 photo takes up more storage and bandwidth than a 640 × 480 version of the same image. The file size also depends on the format (JPEG, PNG, etc.) and compression level, but fewer pixels always means a smaller file.

What format should I save the resized photo in?

JPEG is best for photos you are sharing or emailing because it compresses well and most devices open it. PNG is better if you need transparency or are storing the photo for editing later. Use the format that the website or person asking for the photo specifies.