Two important terms you need to know and it’s not just DPI. The first is that Resolution (DPI) plus Pixel Dimension equals file size.
Why is that important?
Well, it has to do with the second term you need to know. “DPI” (resolution) is important for you to use but more importantly, what file size do you need, using a dpi of 72. Again, file size is determined by resolution and pixel dimension (height/width).
Below are some suggestions on file sizes to use for different types of Internet uses:
Blog
I would suggest that you use a file size no more than 150K for headshots. With images such as artwork or book covers, I would use somewhere between 250-300K. You may have to create a file that size. You will then need to bring the image into your image processing software (i.e. Photoshop), go to file size and enter 72 into resolution and then play around with pixel dimension until you get the file size you want or need.
Images to a friend/someone else, other than competitions.
I usually create my artwork images with a file size of somewhere between 1.5MB and 2.0 MB. Most Internet connections are able to handle this size and more importantly the Internet connections today can handle more than one image at a time. I am assuming however that you are sending the image(s) as an attachment to your email.
Website
The file size is dependent on the website builder you are using. I use WordPress and a theme specifically built for photographers. In this theme, file size is dependent on what you want to accomplish. If I want an image that doesn’t change size, then I can upload an image up to 10MB. To upload an image that can enlarge, if you click on it, I can’t use more than 2MB.
What I am saying is that you have to know the image size requirements for whatever website builder you use which include the online galleries. Again, if you don’t have file(s) in the size you need, you will have to go into your image processing software and the file(s).
Social Media
If it is a headshot or some icon that you need to upload, use a file size of around 150K. If it is for artwork or something of that sort, I would suggest that you use a file size between 1.7MB and 2 MB. The image will probably show large but I want people to see my artwork with detail, so that size does well for me.
Competitions
Follow their competition requirements. They will supply requirements that are in dpi as well as in pixel dimension. For example, “Image(s) should be 72 dpi and no more that 1000 pixels in either height or width.” The most important thing is to follow their requirements. If you don’t, you run the risk of your submission being rejected.
These file sizes are not cut in stone. They are file sizes that have been successful for me. In the end, the choice is up to you, but consider what the image will be used for. That will go along way in what you decide to use as file size, not just “dpi.”
Ed Wedman is the co-founder of Exhibitions Without Walls for Photographers and Digital Artists, online-juried competitions and exhibitions. Under the name of Arthur Jacob he is also an abstract photographer and digital artists. His work has been show in several group and solo exhibitions as well as winning several regional and national awards.
