How to Reduce Pixel Size of an Image

A picture that is 4,000 pixels wide is the wrong size for a box that only shows about 800. If you need to know how to reduce pixel size of an image, change the width and height. That job is different from making the file take less space.

A pixel is one tiny colored square. Width counts the squares from left to right. Height counts them from top to bottom. An image listed as 1200 × 800 is 1,200 pixels wide and 800 pixels tall.

What the two numbers mean

Those numbers are the pixel size. They are not the file size. File size is the KB or MB stored on disk. You can make the file smaller and leave every pixel in place. You can also use fewer pixels and still have a heavy file if the format keeps a lot of detail.

On this site, after you turn resizing on, you can read Original dimensions and Planned new dimensions. The planned pair is the size you are about to save. Check it before you compress.

How to reduce the pixel dimensions

1. Open the image compressor and add a JPG, PNG, or WebP.
2. Open Advanced Settings and find Resize Image.
3. Turn on Enable Image Resizing. It stays off until you turn it on.
4. Leave Maintain Aspect Ratio checked. Type the width you want. The height updates so the original shape stays.
5. Read Planned new dimensions. When the numbers are the ones you want, click Compress Image.
6. Download the file. The name ends with “-compressed”.

Reset to Original Size restores the width and height boxes. You can also leave resizing off and only compress. That keeps the pixel size and tries to store the same grid in a smaller file. Those file-size steps are in how to reduce image file size.

How resizing differs from compression

Resizing changes how many pixels you keep. Compression changes how those colors are written into the file. A JPG at lower quality often uses less disk space because some fine detail is dropped. The count of squares across and down can stay exactly the same.

If you type a larger width, you are making a bigger picture, which is the opposite of this task. The tool’s “Allow resizing to reach target size” option never enlarges a photo. It only reduces pixels after quality alone cannot hit a file-size goal, and only if you turn that option on.

Pick the change that matches the goal

How the shape stays or stretches

Aspect ratio is the shape: wide, square, or tall. Maintain Aspect Ratio keeps it. Turn that box off and you can type a width and height that do not belong together. Faces and logos can look stretched. The page warns you when the lock is off.

A 4,000 × 3,000 photo has the same shape as an 800 × 600 photo. Both are four across for every three down. The smaller one has far fewer pixels. If you later display it at the old size, it looks softer, because the missing pixels are not stored anywhere.

When fewer pixels are the right choice

Use a smaller pixel size when the picture will be shown small. A form thumbnail, an email signature, or a narrow column does not need a 4,000-pixel original. A photo that will sit about 800 pixels wide can be saved near that width.

Keep the full pixel size when someone may print the photo or crop it later. Make the small copy for the upload. Leave the large original alone.

On a Mac, Preview can change pixels too: Tools, then Adjust Size, with Resample image on. That is a different app. The Mac steps are in how to reduce image size on Mac.

What fewer pixels do to the picture

Less detail is the trade. Fine text, hair, and thin lines show it first. Judge the comparison at the size you will really use. A photo that looks soft when you zoom in can still look clear inside a small box.

Compression can soften a photo too, even when the pixel size never changes. If the picture looks worse and the dimensions stayed the same, raise the quality. If it looks worse and the dimensions dropped a lot, type a larger width and compress again from the original.

A chosen pixel size does not guarantee a chosen file size. A flat logo can be tiny. A detailed photo at the same width can be much larger. When you also have a KB limit, set the width and then use a target such as compress an image toward 100KB. Read the status. The number on the card is the real file.

Mistakes that hurt the photo

Making the width larger when you meant to make it smaller. Read the planned dimensions.

Forcing both numbers with the shape lock off. Leave Maintain Aspect Ratio on unless you truly need a new shape.

Shrinking a screenshot until the words blur. Stop while the text can still be read.

Saving over and over from the last download. Each pass starts from a weaker picture. Return to the original when you try a new width.

Assuming the original file changed. The download is a separate file.

Questions

Does a smaller pixel size always mean a smaller file?

Often, but not by a fixed amount. The format and the amount of detail still matter. Read the file size after you compress.

Are resolution and pixel size the same thing?

On a screen, people usually mean the width and height in pixels. Print resolution, in pixels per inch, is a separate number. Changing that print number by itself does not remove pixels.

Can I set only the width?

Yes. With Maintain Aspect Ratio on, the height follows the original shape. You do not have to calculate it.

Will the smaller image look blurry?

It can, if you show it much larger than the new pixel size. At the size you planned, use the comparison as your check.

Do I still compress after resizing?

Yes, if you also want a smaller file. Resizing sets the pixels. Compression stores that picture. One download can include both, as long as resizing was on before you pressed Compress Image.

Keep a copy at the size you will show

Set the width, confirm the height, and look at the picture. Download that copy for the page or the form. Leave the full-size original in place until you know you no longer need those extra pixels.