When you resize an image you change the number of pixels. In computer world this is how it is done - there is no inches or centimetres. But when you print out an image the printer uses a resolution that is expressed in DPI (dots per inch). Setting up DPI or the inch size for screen images makes little or no sense. And when an image is printed you can clearly see that the picture has a size in inches. How do pixels, DPI, and inches go together?
An example: an image should be printed as 6x4.5 inch in 300 DPI resolution. What should be the size of the image in pixels?
It is important that you need to set both values DPI and size. Mihov DPI to Pixel Calculator will suggest the size for your resizing, but you can choose your own. The program does not resize images, use Mihov Image Resizer to do that job.
If the exact DPI/size is not an absolute requirement (for example by your printing house), then you should probably avoid any resampling. All printers should be able to resize the image into desired size.