With Resolution Calculator you can find out:

• Which resolution you should use when you scan the image for the specific halftone screen
• The size you can get for the printout of your digital photograph
• The pixel dimension and the document size in the specific resolution and in the specific color depth (lineart, grayscale, RGB, CMYK)
• The number of shades in the specific printer resolution

It was made for educational use to compare resolutions and image sizes. It may not be very useful for experienced graphic designers but it is useful to beginners.