The Best Size for a Digital Art File

Why worry about the size of your artwork? Many document and art programs have simple ways to reduce picture sizes so getting your art smaller is not a problem. But if you are going to send your artwork to a gallery for review there a few things to consider.
Working with jpegs of your art and simple photo editing program is sufficient for this process. You might want to consider an art program like Adobe Illustrator or Photoshop if you want to do more complex manipulation. But there may be no need if you normally work with real paints and brushes rather than virtual ones.
If the artwork is to be viewed as a whole it should be in the range of what fits the width of a computer screen without having to be enlarged. The goal for this would be about 800-1000 pixels wide. A smaller file will look pixelly if enlarged to fill a screen.
For detail shots of the art work use the cropping tool. Rather than sending a huge file of the entire painting or drawing, crop a section that looks interesting and save it at a fairly large size, a width of 640pixels is considered a large web picture but won't totally fill the screen.
Next if you want to send a preview of your art in an email use a pixel width of about 314 or less. This is considered large for an email but won't fill the screen and you may have a better chance of not getting blocked because of it's reasonable size.
Recently the favicon has become popular. Those are the tiny logos next to site names in your favorites list. The size for that is really small, in some cases only 16x16 pixels total is all you need.
Here are some standard sizes in pixels:
Large document 1024x1024
Small Document 800x800
Web large 640x640 (see the cowgirl at the bottom of the blog)
web small 448x448
email large 314x314
email small 160x160
favicon 32x32 or 16x16