How to Calculate Image Size and PPI when Printing

A man using a printer at home. — There's more to using a digital camera other than simply taking photos; your images can be transformed into works of art. Eugenio Marongiu / Getty Images/Image Source

You bought a fancy digital camera and now you want to print top quality photos. A digital camera is a complex device that if used properly, can give you sharp, beautiful photos. Read the tips listed below and learn about how to calculate image size and PPI when printing.

What is PPI? The first step to understanding how to print high-quality photos is to understand pixels per inch (PPI). The pixels on your digital camera or computer screen get converted into dots on the printed photo. The more pixels you have per inch (centimeter), the sharper your photos will be. A general rule of thumb is to try to have a PPI of between 200 and 400 [source: Colorama].
Size and Pixel Count In order to print a high quality photo, you must first determine the size you want to print. Then check the pixels of the image you want to print. To find the pixel count on your photo, open the image on your desktop computer. Click on File on the toolbar. Select Properties from the dropdown menu. The Properties dialog box that opens will provide you with the details of the photo, including the pixel count [source: HD]. Once you have these two pieces of information (the print size and the pixel count), you can calculate the PPI and determine the resolution of the image.
Calculating PPI The basic equation for calculating PPI is: PPI = width(pixels)/ width of image (inches); PPI = height(pixels)/ height of image (inches). So, for example, if you want to print a 4-inch-by-6-inch image, and your pixel count is 800 x 1200, you need to divide 800 (the pixel height) by 4 (the photo height) and then divide 1200 (the pixel width) by 6 (the photo width). The PPI will be 200, providing you with good quality photos. However, if you want to print a larger photo, for example 8-inch-by-10-inch photo, the PPI reduces to 100 for width and 120 for height, giving you lower quality prints [source: Colgate].

Remember, you can always improve the quality of your photos by putting your camera's MP setting higher. Your photos will take up more room on your memory card, but you'll be able to print larger and sharper photos [source: HP].

PPI FAQ

How many pixels is an inch?

PPI means pixels per inch and differs based on the medium on which it is being displayed. A 1080p screen, for example, has 300 PPI. Typically 1 inch equals 96 pixels, 2 inches are 192 pixels, 3 inches are 288 pixels and so on.

What is 1920x1080 pixels in inches?

This depends on the size of a 1920x1080 pixel screen. For example, a 20-inch 1680x1050 pixel screen would mean 5 inches wide while a 1920x1080 would show as 5.75 inches wide.

How do you convert PPI to DPI?

PPI and DPI are usually equal unless you opt to change the same in settings. Typically, DPI (dots per inch) is the number of dots a printer makes per inch on a page when printing. The higher the DPI, the better the quality.

What is the best pixels per inch for printing?

More PPI means the more detailed the picture will be. The best print quality you can get is on 240 or 300 DPI. Your PPI should be higher or equal to the DPI you are choosing to print with.

Is 300 PPI the same as 300 DPI?

DPI and PPI are usually used interchangeably, even though both are completely different. The confusion stems from the fact that 300 DPI on paper is equal to 300 PPI on screen.