University of Wisconsin–Madison

Resizing Images


Images have three basic dimensions:

  • height and width
  • resolution


Resolution is the amount of data originally captured.  We measure resolution in pixels per inch. 

Whatever resolution you capture the image at, you’re stuck with. You can’t increase resolution (add data), only decrease it (throw data away).

When capturing an image, consider how you want to use it:

  • for print, capture at 300ppi or better
  • for screen display only, capture at 72ppi

The higher the resolution, the larger the image’s filesize, so capture devices may default the capture resolution to 72dpi to save space.  Always check your resolution before capturing an image.

What to do if You Didn’t Capture the Image

Often you may be working with an image someone else captured.  There’s an easy way to check the file dimensions to learn whether the image is large enough to print, or too big for the Web:



Right‐click the photo and choose Properties from the popup menu. The Properties window appears.

Click the Details tab.

Scroll to the Image section:



…and look for the horizontal and vertical resolution.

Right‐click the photo and choose Open With..Preview.

The photo opens in the Preview ap.

From the Preview menu, choose Tools..Show Inspector.

The General Info screen appears:


Look at the Image DPI setting.

Downsizing an Image on the Screen

Word, PowerPoint, and WordPress all let you resize the image on the screen by clicking and dragging the borders.

Don’t do this in WordPress!

Downsizing images on the screen does not affect the size of the file – only the way it appears on the screen.

If the file size is large, it will eat up more storage space and download slowly on wireless devices.

Here’s how big a difference we’re talking about:

Image Meant For:

Final Resolution:

Storage Space Needed:







Here’s an Easy Way to Downsize Images for the Web

Trying to understand resolution and image dimensions can give you a headache.

A much easier way to downsize images is to use Web Photo Resizer.

Go to this website:

Upload your image and resize it so the width is 585 or less pixels wide.  Click “download this image” and save the resized image to your hard drive.