Image Sizes, File sizes and DPI

When we use the word “size” in relation to an image it can be quite confusing as it can mean at least three different things.

Image Sizes, File sizes and DPI can easily get mixed up. So ensure, when talking to others, you are talking about the same thing.

  • It can be the file size, the amount of space it takes up on your hard drive measured in kilobytes and megabytes.
  • It can be the physical size the picture is printed out (measured in cm or inches)
  • It can be the size in pixels (explained more below)
Image Sizes, File sizes and DPI

Image Sizes, File sizes and DPI

DPI

This stand for Dots per Inch and although it sounds complicated it is actually quite simple. It is a measure of “resolution”… how detailed the picture is. A picture which is 300 dpi will have a lot more fine detail than a picture which is 72 dpi. That is why cameras with high dpi are popular! In the end there are only 3 basic resolutions.

  • 72 dpi This is normally seen as the standard for images on the web. In fact the actual DPI does not matter just the number of pixels for width and height but if you stick to 72 dpi for web images they will be easier to compare. 72 dpi produces images with small file sizes and therefore they download quickly.
  • 150 dpi this resolution is good for general printing, backing papers, cartoon images etc. Although not the highest quality it is high enough for these types of images.
  • 300 dpi. Its a fine resolution for printing photos… can also be used for finer detailed craft papers.

So taking that into account many craft papers can be made at 150 dpi. If we wanted to make an A4 sheet at 150dpi it would be

150 x 8.3″= 1245 pixels  by 150 x 11.7″ =1755 pixels

So an A4 sheet at 150dpi would be 1245 x 1755pixels

Image Sizes, File sizes and DPI

Authored By: Bob Prentice

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